Focus on California 8th Grade Physical Science Textbook Chapter 6 Chemical Reactions

Chapter Chemical Reactions Standards Preview ( reactions are processes in which atoms are rearranged Into nations of molecules . As a basis lot understanding this concept Students know reactant atoms and molecules to form products with different tal . Students know the Idea ol atoms explains the tion of matter . In reactions the number of atoms stays the same no matter how they are arranged . so their total mass stays the same . Students know chemical tions usually heat or absorb heat . progress is made by asking meaningful questions and conducting careful tions . As a basis for understanding concept and addressing the content in the other three strands . students should develop their own questions and perform . Students will Plan and ( a to test a hypothesis . Evaluate the a ( ura ( and reproducibility of data . Sums fly as sodium metal reacts with water

, Preview Scion ! Chemical Reactions What happens during a chemical reaction ?

Check What You Know Suppose you fill a sealable bag with ice cubes , and you allow the ice to melt . How would the mass of the bag and ice before melting compare to the mass of the water and the bag after melting ?

Explain your answer .

Vocabulary The images shown here represent some ol the terms in this chapter . Vou can use this vocabulary skill to help you understand the meaning of some key terms in this chapter . Identify Multiple Meanings some familiar words have more than one meaning . Words you use everyday may have different meanings in science . Everyday Meaning I Scientific Meaning concentration . Close attention along The of a substance in a given period of time volume Example Studying with the Example Most soft a high on her concentration concentration of sugar . The subject at discussion , Anything that has mass and takes up concern . or ( space Example The subject matter of Example Solids , liquids , and gases are the movie was space travel . states of matter . Anything that IS made or A substance formed as a result or a created chemical reaction Example Mill and cheeses are Example In a chemical reaction , substances dairy products . can combine to form one or more . Apply Complete the sentences below with the correct word from the list above . Then identify the terms that have meanings . The coed told the turn to keep its during the game . Seawater has a high of salt .

Chapter Vocabulary Section I am matter chemistry physical property hre , chemical property ( hangs ( hang product ! exothermic Section ling mi equation conservation of matter open system closed synthesis decomposition replacement Section activation energy ( an ( analyst Enzyme Section long ( fuel ' Build Science Vocabulary Online Visit Web ( ode 111

' Take Notes Science chapters are packed with information . Each section needs to be read at least twice . After finding the main idea and important details , take notes so you have something to study . In your notebook . create a organizer Label the left side Recall Clues and Questions , Label the right side I Under Notes , write key ideas , using phrases and . Include a law important details . Use your notes to write a summary statement for each red heading . I Under Recall Clues and , write study questions . As you take notes . think about the key concepts and key terms ID the . Look at the example for Se ( tion I In this ( Recall Clues Questions What I miner ?

How can matter be described ?

Apply It ! Notes Matter anything that hao mar and takes up space Properties of matter I Physical ' bailing palm . solar . hardness I , ca rust . or . Manor can be described In terms at and properties . What are two lmportant ideas found in the notes above ?

What questions in the left help you recall the Take notes as you read eath section in this chapter , Standards Investigation Demonstrate Conservation of Matter when water evaporates , it is not destroyed or lost . In fact . matter is never created or destroyed in either a physical change or a chemical reaction In this investigation , you design and build a closed structure in which a chemical reaction can occur . You will use the chamber to confirm that matter Is not created or destroyed in a chemical reaction . Your Goal To design and build a closed chamber in which sugar can be broken down Your structure must be made oi materials that are approved by your teacher be built to specifications agreed upon by the class be a closed system so the masses oi the reactants and products can be measured be built following the safety guidelines in Appendix A Plan It ! Before you design your reaction chamber , find out how sugar can be broken down . Next , brainstorm with classmates to determine the safety features of your chamber . Then choose materials for your structure and sketch your design . When your teacher has approved your design , build and test your structure .

, Standards 854 Students know reactant atoms and interact to farm products with chemical properties . Students know chemical reactions usually heat or absorb heal . How can ( in mailer be described ?

reaction Key matter I chemistry How can you tell when a chemical I physical property I chemical property I change I chemical change I ri . product precipitate I endothermic reaction I ( 214 lead to ii treat . Observing Chemical Change How Does Matter Change ?

Put on your safety goggles , Place small spoonfuls of baking soda into a clear plastic cup . Holding the cup over a large bowl or sink , add about 125 of vinegar . Swirl the cup gently . Look at the material in the ( up . What changes do you see ?

Feel the outside of the ( up . What do you notice about the temperature ?

Carefully fan the air above the liquid toward you . What do you smell ?

think It Over Observing What ( did you detect using your senses of smell and touch ?

Picture yourself river El . You see burning change from hard solids in still pile of ash . You popping and lira am the wood burns . You ( You feel the hunt on your skin . illy . you taste the results . The crisp of the toasted marshmallow tastes quite from the soft surface marshmallow just out of its hag . skin . and ' are all of . Matter is that has and up space . The study of how is called chemistry .

Matter and Change Part of chem is describing . When you describe ter . you explain its characteristics . or properties . and how it changes . Figure lists some of the properties of water . Recall that matter can he described in terms of two kinds of properties and chemical properties . Changes in matter be described in terms of physical changes and chemical changes . Properties of Matter A physical property is a tic of a substance that can be observed without changing the into another substance . The at which solid melts is a physical property . For example . ice melts at a temperature of degrees Celsius . Color . hardness . texture . shine . and are some other physical properties of matter . The ability of a substance to dissolve in water and how well it conducts heat and electricity are examples ol still more properties of A property is a characteristic of a substance that describes its ability to change into other To observe the properties of a substance . you change it to another substance . For example . when magnesium burns , it combines with oxygen in the air , forming a new substance called oxide . The chemical property of being able to burn in oxygen is called flammability . Other chemical include a material ability to rust or tarnish . FIGURE Properties at Water This geyser gives of ?

hot water and water vapor , which condenses into a visible ( loud in the cold air . The temperatures at which water boils and freezes are properties of water . How will the snow ( hang when spring arrives ?

Properties at Matt at moms and oxygen new I Does not burn In I no rule Reacts with some Clean . colorless liquid at room I Boil at 100 ' menus or are Ounces in Matter Matter can undergo both physical change and chemical change . Observing Change . In a plastic bag . add 10 of calcium chloride and 10 of baking . Carefully lower a small paper cup containing 30 . 01 water into the bag . Squeeze out any excess air from the bag , and then seal it . Tip over the bag so that the water spill out of the cup and mixes with the calcium chloride and baking soda . Record your observations on a sheet of paper . Inferring Did you observe a physical change or a chemical change ?

Explain your answer . 216 Change Von can flatten and pull on a marshmallow but its composition will any the me . change If you toast . the mom and other will cook or burn . producing I crust mode of new Changes of Matter Like properties of matter . changes in matter can be physical or chemical . A physical change is any change that alters the form or appearance of a substance but ' not make the into another substance . For example , when you squash a marshmallow . you cause a cal change . The shape of the marshmallow changes but not the taste . still made of the same compounds that have the same . in a physical change . one or more physical ties of the are altered , but the chemical composition remains the sauna . Bending , crushing . breaking , and cutting are all examples of physical changes . Changes of static . such as melting . freezing , boiling . and condensing . are also physical changes . Sometimes when matter changes , its chemical composition is changed . For example . the trust on toasted is the result of sugar changing to a mixture of diflerent substances called caramel . A change in matter that produces one or more new substances is a chemical change , or chemical reaction . In a chemical change . the atoms are rearranged to form new with different chemical and ) al properties . The substances that undergo change in a chemical reaction are called reactants . The new substances formed by the reaction are called products .

Bonding and Chemical Change Chemical changes occur when bonds break and new bonds form . result . substances are produced . You ) that atoms ' when or . pit MA in Figure hath at bum ! i ' a . Isit . ig and oi . web ( ode , gas ) in the air of . made two oxygen that chart . hands arc , with ( lurch it ' two of ils In an oxygen atom . The , atom negative ion . and the atom ( inn . than ( i ( charged . i ( band form and 01 ions , The ionic ( I is , um ! is . I , crumbly properties that differ trom those of How shiny For . Bonding and at About , it talus A bums , bond more than . to melt oxide . en 310 new bonds form , The reaction gives off energy . interpreting Diagrams Why does the oxygen ion have a charge ?

i What are two properties of magnesium oxide ?

Oxygen bonds break . An oxygen oxygen molecule has A atom can Accept double bond two electrons Magnesium and Magnesium oxygen ma Magnesium and oxygen ( A magnesium atom loses two An ionic bond forms ta an oxygen atom the oppositely charged ions charged Ions . Chapters 117

From Evidence for Chemical Reactions Many kinds of change provide evidence that a chemical reaction has occurred . Applying Concepts What other evidence might tell you a chemical reaction has occurred ?

11 ! Evidence for Chemical Reactions How can you tell when a chemical reaction occurs ?

You need to look for clues . Chemical reactions involve changes in properties and changes in energy that you can observe . Oranges In Properties One way to detect chemical tions is to observe changes in the properties of the materials involved . Changes in result when new substances ( Figure shows some examples . For instance . a color change may signal that a new substance has formed . Or . the ing of two solutions may yield a precipitate . A precipitate pree SIP uh ) is a solid that forms from solution during a cal reaction . Another observable change is the formation of a gas from solid or liquid reactants . Physical properties such as texture and hardness may also change . For example , moist bread dough forms a dry , porous solid after baking . Two clear liquids react . A a precipitate . The light green leaves oi early spring slowly tum darker as chemical reactions in the leaves produce more of the green compound chlorophyll .

Changes in physical properties can be easy to spot as change into products . But what about the chemical ?

atoms and molecules interact to form products with different chemical properties . For example . sodium ( Na ) and chlorine ( react to form an ionic compound . sodium chloride ( Both reactants are very reactive elements . ever , the product , sodium chloride , is a very stable compound . Although you may observe a property change in matter , the change does not always indicate that a chemical reaction has taken place . Sometimes physical changes give similar results . For example , when water boils , the gas bubbles you see are made of molecules of water , just as the original liquid was . The sign of a chemical reaction is that one or more new substances are produced . For example , when an electric current is passed through water during electrolysis , two new substances are , hydrogen gas and oxygen gas ( 01 ) How is a precipitate evident for I ' tE radian ?

A golden loaf of bread with its crust has very different properties from the soft dough that went Into the oven i This Activity Mostly Cloudy . Put on your safety goggles and apron , Pour about of into a plastic cup . Pour an equal amount of plain water into another plastic cup . Add about of carbonated water to each of the cups Drawing In which ( up do you think a chemical reaction attuned ?

What evidence supports your cone ?

Oxygen bubbles that form during photosynthesis collect on the leaves of a plant . chapters 219 hour Reactions When you try an egg , it absorbs energy . The reactions that occur are endothermic . Interpreting Photos What properties of the egg change as it cooks ?

Energy can change egg whites from a clear liquid into I white solid . Oranges in Energy As mutter changes . it can either release energy . reactions usually absorb or heat . hie common indication oh iii is a iii . if you did the Standards ii . you observed that the ) colder . When baking soda ( sodium bicarbonate ) reacts with . the reaction absorbs heat from the solution . it feel . Recall that ii reaction occurs when ) and new bonds form . bonds between atoms requires energy . Making a releases energy . In an reaction duh ' mik . the total and oi results in 21 net absorption of energy . The energy is absorbed as heat from matter . which tools . The reaction of baking soda and vinegar is endothermic . During the reaction . energy is absorbed . causing the to cooler . However , do not result in zi decrease in . Many ' occur only when heat is constantly added . For example . the reactions that when you fry an egg are . Reviewing Math Algebra and Functions Analyzing Data Energy in Chemical Changes while the substances react . The student the graph at right . time the temperature was ?

minutes ?

Interpreting Data Is the reaction endothermic or exothermic ?

Explain . reaction stop ?

How can you tell ?

2200 A student places two substances in a flask and measures the temperature once per minute the time and temperature data and creates . Reading Graphs What was the temperature in the flask at minutes ?

When was the lirst . Calculating How many degrees did the temperature drop between minutes and At what temperature did the Energy of a Chemical Reaction plots Temperature ( I ) Drawing Conclusions Suppose the temperature in the flask increased instead of decreased as the reaction occurred . In terms of energy , what kind at reaction would it be ?

Explain .

Jim ii An Reaction Enough energy is released by the burning at airplane met to keep a plane moving fast enough to fly . In an exothermic reaction ( elt soh ' the total and breaking of hands results in net ise of energy . The energy is typically i as heat into nearby matter . For example , the reaction fuel and in an airplane releases . mostly in the form of heat . The heat muses gases in the to . The and of the gases out of the plane exert a force that moves the plane . Rand . What is In endothermic reaction ?

Section Vocabulary Skill Identify Multiple Meanings Review the twu of the ward . Then use iii a sentence . Reviewing Key Concepts a . Explaining ' is the phi ca and the chemical properties of it substance ?

Posing Questions When silver are in ancient , they are coated with black ( rust . question ( you ask to help you decide whether the silver ( lE ! a change ur a physical change ?

Making Generalizations of chemical bonds and , what of occur between ! when undergo ?

365 Assessment . Reading . Writing a . Listing What kinds can use to i determine if at chemical reaction ?

interpreting Photographs How do the uf the egg ( in Figure differ from the properties of raw ?

Comparing and Contrasting How an and the ?

How are they ?

in Science Letter Imagine you have a pen pal who is studying chemistry just like you are . Your pen pal claims the change from liquid water to water vapor is a chemical . Write a brief letter that might convince your pen pal otherwise . Chapters 0221 Where the Evidence ?

Problem , What are some signs thata reaction has is I we . take DRE ?

a pee in pi eo so rum ca na em a clean plastic cup . Record in the data table the appearance of the sodium carbonate . Observe a dropper containing hydrochloric acid . Record the appearance of the acid . acid can burn you or Skills Focus observing . predicting , drawing conclusions Materials anything else it touches . Wash spills small ( ups with water ' Make a prediction about how you think the . su acid and the sodium carbonate will read . when mixed Record your ( day . Add about 10 drops of hydrochloric acid to . the sodium . Swirl to mix the , sodium cabana ( sow ) term of the cup . Record your observations . graduated cylinder . 10 PART aluminum foil , about square dame ( in a borne . Fold up the sides of the aluminum foul square . owe , sun , to make a small tray . sodium carbonate solution . Use a plastic spoon to place a pile of sugar into the tray . Carefully describe the appearance of the . Preview the steps for each reaction and copy the saga In your dam a data table into your notebook . Data Table Observations Observations Mamba During Reaction After Reaction Observations Before Reaction . carbonate I I Reaction ( acid . Copper sodium carbonate . Sugar hat I I ! 2210

. Secure a small candle on your desktop in a lump of clay . Carefully light the candle with a match only after being instructed to do so by your teacher . CAUTION Tie back long hair and loose clothing . Predict what you think will happen if you heat the sugar . Record your prediction . 10 . Use tongs to hold the aluminum tray . Heat the sugar slowly by moving the tray gently back and forth over the flame . Make while the sugar is heating . 11 . When you think there is no longer a chemical reaction occurring , blow out the candle . 12 . Allow the tray to cool for a few seconds and set it down on your desk . Record your of the material left in the tray . 13 . Put about of copper sulfate solution in one cup . CAUTION Copper sulfate is ous and can stain your skin and clothes . Do not touch it or get it in your mouth . Put an equal amount ol sodium carbonate solution In another cup . Record the appearance ol both liquids . 14 . Write a prediction of what you think will happen when the two solutions are mixed . 15 . Combine the two solutions and record your observations . CAUTION Dispose of the solutions as directed by your teacher . 16 . Wash your hands when you have working . Analyze and conclude . Predicting How do the results of each reaction compare with your predictions ?

Observing How did you know when the reaction in was over ?

Interpreting Data What was the evidence ol a chemical reaction in Part ?

In Part . Observing Was the product of the reaction in Part a solid , a liquid . or a How do you know ?

Drawing Conclusions How do you know it new substances were formed in each reaction ?

Communicating Make a table or chart briefly describing each chemical change in this lab , followed by the evidence for the chemical change . More to Explore Keep your data table handy as you read the rest of this chapter . As you learn more about cal reactions , try to the products that formed in Parts , and ol the Skills Lab . Research the physical properties of each product by using your library or the Internet . Evaluate the accuracy of your data by comparing the properties of the substances produced in the lab to the properties that you found in your research . crime 223

0000 ( Standards Focus Students know the idea ol atoms explains the conservation ol matter . In chemical reactions the number of atoms stays the same no matter how they are arranged , so their total mass stays the same . what does in chemical equation How is matter conserved during a chemical reaction ?

what must a balanced chemical show ! What are three types ol chemical reactions ?

KEY chemical equation I conservation ol matter Describing Chemical Reactions . Lose Anything ?

Place about two dozen coins on a table . Sort them into stacks ol pennies , dimes , and quarters . Count and record the number of coins in each stack . Calculate and record the value ol each and the total of all stacks combined . Mix all the coins together and then divide them randomly into four unsorted stocks . Again calculate the value at each stack and the total amount of money . Count the total number of each type of coin . Repeat Steps and . Think It Over Making Models What happened to the total value and types of coins when you rearranged them ?

Did rearranging the coins change the properties of any coin ?

It you think at the coins as each representing a different type of atom what does this model tell you about chemical reactions ?

I open system I closed system ' 59 ' You look at your cellular phone display and read the ?

You . Mal ! I decomposition are short for Du you want to get some tonight ?

and No . tomorrow ( See you Cellular phone use and lu ideas in shorter form . A type of is used too . molecules react with oxygen to form waiter is a ' way to describe the and oxygen . And writing it is slow . Instead , often ' in plaice . I replacement A message on a cellular display 224

What Are Chemical Equations ?

A chemical equation is a short , easy way to show a chemical reaction , using symbols instead of words . Although chemical equations are shorter than sentences , they contain more mation . Chemical equations use chemical formulas and other symbols instead of words to summarize reaction . Using Formulas All chemical equations use formulas to resent the substances involved in a reaction . You may recall that a chemical formula is a combination of symbols that represent the elements in a compound . For example , is the formula for carbon dioxide . The formula tells you that the ratio of bon to oxygen is to . Carbon dioxide is a molecular pound . so it is made up of molecules . Each carbon dioxide molecule has I carbon atom and oxygen atoms . Figure lists formulas of other compounds that may be familiar to you . Structure of an Equation All chemical equations have a common structure . A chemical equation tells you the stances you start with in a reaction and the substances you get at the end . The substances you have at the beginning are the reactants . When the reaction is complete , you have new stances called products . The formulas for the reactants are written on the left . lowed by an arrow . You read the arrow as yields . The las for the products are written on the right . When there are two or more reactants . they are separated by plus signs . In a similar way . plus signs are used to separate two or more . Below is the general plan for a chemical equation . Product Product The number of reactants and products can vary . Some tions have only one reactant or product . Other reactions have two , three . or more reactants or products . In Figure you can see the equation for a reaction that occurs when limestone ( is heated . Count the number of reactants and . and familiarize yourself with the pans of the equation . Reactant Products ' yields Symbol formula . Flaunt The formula of a compound identifies the elements In the compound and the ratios in which their atoms are present . Formulas oi Familiar Compounds compound Formula Carbon dioxide Methane Propane Sugar ( sucrose ) Rubbing alcohol Ammonia Sodium chloride Baking soda , Fawn A Chemical Equation Like a building . a chemical equation has a basic structure . interpreting Diagrams What does the subscript in the formula for calcium carbonate tellyou ?

ons Fe Iron Mon conservation of Matter Matter is conserved in chemical reactions . em . Activity is Matter Conserved ?

Add water to a small , container until it is full . Measure the combined mass of the partially filled container . its cap , and one quarter of an effervescent tablet . Drop the tablet into the water , and immediately screw on the cap . After the stops , measure the mass of the sealed container . Remove the cap . Measure the combined mass of the unsealed container . its contents , and the cap . Interpreting Data How did the mass measured in Step compare to the masses measured in Steps and ?

Was matter conserved ?

Iron Sulfide Conservation of Matter Look closely at the values for mass in Figure . Iron and sulfur can react to four ) imn . The photograph represents a principle tirst demonstrated by the French chemist Antoine in 1774 . This principle is called of matter . It states that . during a chemical reaction , matter is neither created nor destroyed . The total mass of the reactants must equal the total mass of the products . Conservation of Mama The idea of atoms explains the of matter . In chemical reactions . the number of atoms stays the same no matter how they are arranged . So . their total mass stays the same . Look again at Figure . Suppose one atom of iron reacts with one atom of sulfur . At the end of the reaction . you have one iron atom bonded to one sulfur atom in the compound . All the atoms present at the start of the tion are present at the end of the reaction . The amount of matter does not change . The total mass stays the same before and after the reaction . Open and Closed Systems At first glance . some reactions may seem to violate the principle of conservation of matter . not always easy to measure all the matter involved in a reaction . For example . if you burn a match , oxygen comes from the rounding air . But how much ?

Likewise . the products escape i into the air . Again . how much ?

A burning match is an example uf an open . in an open system , matter can enter from or escape to the ings . The burned uut fire in Figure 10 is another example of an open system . If you want to measure all the matter before and alter a reaction . you have to be able tu contain it . In a closed system . manor is not allowed to enter . The pear decaying under glass in Figure 10 is a closed system So is a chemical reaction inside a sealed plastic bag . What Is a closed system Flaunt to Open and Closed Systems A wood fire is an open system because gases into the air . A pear in a glass dome is a closed system because the reactants and are contained inside the dome . solving What masses would you need to measure before and after a wood fire to show conservation of mass ?

Open System for the ash . products of the wand live have escaped up the chimney or into the room . Closed System The total mass of the pear and the substances produced during its decay are by the glass dome . Fresh pear Decayed pear chapters 0217 Go Online For Balancing Equations activity Web ( ode Balancing Chemical Equations The principle of conservation of matter means that the total number of atoms of each element in the reactants must equal the total number of atoms of each element in the products . GTO describe I reaction accurately , a chemical equation must show the same number of each type of atom on both sides of the equation . Chemists say an equation is balanced when it accurately represents conservation of matter . How can you write at balanced chemical equation ?

Write the Equation Suppose you want to write a chemical equation for the reaction between hydrogen and oxygen that forms water . To begin . write the correct for both reactants and product . Place the reactants . and ( on the left side of the arrow , separated by a plus sign . Then write the product , on the right side of the arrow . 01 Product Count the Atoms Count the number of atoms of each element on each side of the equation . You two atoms gen in the reactants but only one atom of oxygen in the product . hydrogen 310 oxygen atom hydrogen atoms oxygen atoms How can you get the number of oxygen atoms on both sides to be the same ?

You can not change the formula for water to because is the for hydrogen peroxide . a compound . So . how can you show that mass is conserved ?

Use Coefficients to Balance Atoms To balance the equation , you can change the . A ( uh FISH unt ) is a number placed in front of a chemical formula in an equation . it tells you the relative of reactant or it product that takes part in the reaction . In the unbalanced tion written in Step I , the coefficients are understood to be .

You can balance the number of oxygen atoms by changing the to . Now the right side of the equation has two water molecules . each containing an oxygen atom . Unbalanced oa hydrogen oxygen oxygen atoms atoms atoms hydrogen atoms By balancing the oxygen . you unbalanced the number of hydrogen atoms . There are now two hydrogen atoms in the and four in the product . To balance the hydrogen . change of to . All the atoms in the reactants are now accounted for in the products , Balanced A hydrogen oxygen oxygen atoms atoms atoms hydrogen atoms Look Back and Check The equation tells you two hydrogen molecules react with one oxygen molecule to yield two water molecules . The total number of atoms stays the same before and after the reaction . The equation is balanced . Balancing Equations Math . the Equation Data I , Count the Atoms 02 Balancing Chemical Equations Magnesium ( reacts with oxygen gas ( forming magnesium oxide ( Write a balanced equation for this reaction by following Steps through described above , coefficients . Chemical Equations Balance the equation for 33 ' the reaction of sodium metal ( Na ) with oxygen gas ( forming sodium oxide ( Balancing Equations Balance the equation for , the reaction of tin ( with chlorine gas ( tin chloride ( Look Back and Check one

new 11 of Reactions Three categories oi chemical reactions are synthesis . decomposition . and replacement . Making Models How do dine different geometric shapes act as models for elements and compounds in reactions ?

1300 Classifying Chemical Reactions You have already how to classify physical changes such as melting . boiling . and freezing . You can classify chemical changes . too . general types chemical reactions are synthesis . decomposition . and replacement . Synthesis Have you ever listened to music from a sizer ?

You can hear many notes and types of sounds combined to make music . To synthesize is to put things together . In chemistry . when two or more elements or pounds combine to make a more complex substance . the tion is as a synthesis ( SIN sis ) The reaction of hydrogen and oxygen to make water is a synthesis reaction . Decomposition In contrast to synthesis , decomposition occurs when compounds break down into simpler products You may have a bottle of hydrogen peroxide ( 203 ) in your house to clean cuts if you keep such a bottle for a very long time . the hydrogen peroxide decomposes into water and oxygen gas . Replacement When one element replaces another in a pound . or when two elements in different compounds trade places . the reaction is as a . look at this example , Copper metal can be obtained by heating copper oxide with carbon . The carbon takes the place of copper .

Reviewing Key Concepts war , I One element replaces another element in a compound Double Two elements replace each other in compounds . The reaction copper and carbon is called at single reaction because one element . carbon . replaces another element . copper . in the compound . in a replacement , in ( Int compound to it . trade places with ' in another . reaction is an of a res a sect , Use Figure 11 to help you track what happens to elements in types of chemical . Section Assessment Vocabulary identify Multiple Meanings the multiple meaning words . The in traction is called reaction ?

Identifying do the formulas . arrow . and plus signs in at yuu ?

Comparing and Contrasting How are reactants and the in a ?

How are they treated a . Explaining How does the principle of matter ?

Applying Concepts If the total mass of the products of a reaction is 250 , what was ' I ( total uf the reactants ?

033 . Math . Reviewing What are three types of ?

bi Inferring What is the smallest possible uf products in a Practice Balance the following equations . Fe . Oz chapters 9231 ! following reaction ) Technology and Tech Design ' Society . All Bags What moves faster than 300 , inflates in less than at second . and saves lives ?

An air bag , of course ! When a moving car is suddenly stopped in crash . objects inside the car keep moving forward . Death or serious injury can result when passengers hit the hard parts of the interior . Air bags , working with seat belts , can slow or stop a person forward motion in a crash . How Do Air Bags Increase Safety ?

front air bags became a in the seat belts were the restraints for in cars . belts do a great job of keeping people from flying forward in a crash . but even seal bells , some takes place . Air bags were as I second form . They provide buffer a person ind the steering wheel . dashboard . or windshield . Sodium azide pellet Igniter Folded air bag Steering wheel Crash sensor Crash sensor Collision Detected The crash sensor is located toward the front of the car . The sensor detects an impact and sends a signal to the air bag igniter to start the chemical . Alt lag , Nitrogen gas Inflated airbag Pellets of a compound called sodium azide ( are heated . causing a rapid decomposition reaction . This reaction releases sodium metal ( Na ) and nitrogen gas ( which inflate the air bag in about 30 milliseconds . 2310

Cushion or Curse ?

Air bags save of each year . However , if your is too close to the airbag when it , the impact of the expanding bag may do more harm than good . Since ) mum than 20 ! including children . have bun killed bags close to them . Air bags are designed for adults hut a risk to , lightweight adult and children . That is why children should never ride in a front in . They are safer in the sent without air hag than in the seat with air hags Air Bag Tony holes in the fabric of the air bag allow some oi the nitrogen gas to escape , so the bag starts to bythe time a person makes ( with it . In this way . the air bag provides a deflating cushion that slows forward movement . A Car manufacturers must test their vehicles to verify that they meet minimum government safety standards . New cars are required to have air bags on both the driver and passenger sides . Weigh the Impact . Identify the Need Air bags are called mental restraint systems Why is it important to restrain people in a collision ?

Research Us the to learn how bags are being changed , added . and to improve their safety and ) Write unc of new air bag technology and it in paragraphs . Online Visit om Web ( ode Chapter 233 Focus is Students know atoms and interact to with different properties . Students know ( usually liberate or absorb heat Now is energy related to chemical reactions ?

what factors effort the rate of a chemical reaction ?

Key Terms ' activation energy ' I catalyst I enzyme inhibitor Controlling Chemical Reactions , Standards Can You Speed Up or Slow Down a Reaction ?

Put on your safely goggles and lab apron . Obtain three solutions of vitamin and one at room temperature . one at about 75 ' and one chilled to between and 10 ( Add drops of iodine solution to each container and stir each with a clean spoon . Compare changes you observe in the solutions . Clean up your work area and wash your hands . Think It Inferring What conclusion can you make about the effort of temperature on the reaction of iodine and vitamin ?

With a , of lightning strikes at in the forests The lightning splits and sets tire to the on the it . The leaves are dry and ( min . The crackling tire black patch in the ' leap to twigs and on . the forest is , and lurks at true start . unity in an tower . ranger spots ( calls in the meet under certain . In . and Iii just ' But , in , docs not ) burn ily . Yet , once wood docs to burn . it zi steady supply heat and light . Why is it so hard to start and ?

lightning can supply enough energy to ignite I forest .

Energy and Reactions To understand why it can be hard to start some chemical tions . look at Figure . The rock at the top of the hill can fall over the cliff . releasing energy when it crashes into the rocks at the bottom . Yet it remains motionless until it pushed over the small hump . Activation Energy Every chemical reaction is like that rock . A reaction wo begin until the reactants have enough energy to push them over the hump . The energy is used to break the chemical bonds of the reactants . Then . the atoms begin to the new chemical bonds of the products . Activation energy is the minimum amount of energy needed to start a chemical reaction . All chemical reactions require I certain amount of activation energy to get started . Consider the reaction in which hydrogen and oxygen form water . This reaction gives off it large amount of energy . But if you just mix the two gases together , they can remain unchanged for . For the reaction to start , a tiny amount of activation energy is just an electric spark . Once a few of hydrogen and oxygen react . the rest will quickly follow because the first few reactions provide activation energy for more molecules to react . Overall . the releases more energy than it uses . Recall from Section that this type of tion is described as exothermic . hating What is the function of a spark in a reaction between hydrogen gu and oxygen gas ?

Hell ! 12 Modeling Activation Energy The rock at the top of this hilt can not roll down the hill until a small push gets it going . Making Models How is this cartoon a kind of model for the role energy In a chemical reaction ?

Video Held School Chemical Reactions Haunt 13 Energy Changes in Chemical Reactions Both exothermic and endothermic reactions need energy to get started . leading Graphs What does the peak in the curve in each graph represent ?

Reaction and Reactions Every cal reaction needs activation energy to get started . Whether or not a reaction still more energy from the environment to keep going depends on if it is exothermic or endothermic . reactions follow the pattern you can see in the first diagram in Figure iii . The dotted line marks the energy of the reactants before the reaction begins . The peak in the graph shows the activation . Notice that at the end of the tion . the products have less energy than the reactants . This results in a release of heat . The burning of fuel . such as wood . natural gas . or oil , is an example of an exothermic tion . People can make use of the heat that is released to want their homes and cook food . Now look at the graph of an endothermic reaction on the right of Figure 13 . Endothermic reactions also need activation energy to get started . But . in addition . they need energy to keep going . Notice that the energy of the products is higher than that of the reactants . This difference tells you that the reaction must absorb energy to continue . When you placed baiting soda in vinegar in the Standards in Section the thermal energy already present in the solution was enough to start the reaction . The continued by drawing energy from the solution . making the solution feel colder . 395 haveless energy than the products ?

Reaction Activation 7350 Rates of Chemical Reactions Chemical reactions don I all occur at the same , like explosions . are very last . Others . like the rusting of iron , are much slower . Also . a particular reaction can occur at different rates depending on the conditions . If you want to a chemical reaction happen faster . you need to get more reactant particles together more often and with more energy . To slow down a reaction , you need to do the opposite . Factors that affect of reaction include face area , temperature , concentration , and the presence of or inhibitors . Surface Area Look at Figure 14 . The wreckage used to be grain elevator . It exploded when grain dust ignited in the air above the stored grain . Although the grain itself does react violently in ai the grain dust can . This is related to surface area . When a chunk of solid substance reacts with at uid or gas . only the particles on the surface of the solid come into Contact with the other reactant . But if you break the solid into smaller pieces , more particles are exposed and the reaction happens faster . Sometimes . up a reaction this way is dangerous . Other Limes , increasing surface area can be useful . For . chewing your food breaks it into smaller pieces that your body can digest more easily and quickly . Interpreting Data . Measure the length and width of a face of a gelatin cube . Calculate the area of that face of the cube . Ana length width . Repeat for each at the other faces . Then add the six values to get the total surface area . Using a plastic knife , cut the cube in half . Add the surface areas of the two pieces to get a new total . How did the original total surface area compare with the total area after the cube was cut ?

Predict the total surface area it you cut each cube in two again . It you have time , test your prediction . Home 14 Surface Area and Reaction Rate Grain dust reacts explosively with oxygen . Minimizing grain dust in a grain elevator can help prevent an like the one shown here .

15 concentration and Reaction Rate Bubbles of hydrogen gas form when magnesium reacts with acid , The solution heats up quickly , indicating that the reaction is exothermic . Relating Cause and Ethel What makes the reaction faster in the test tube on the right ?

BIO Temperature Another way to increase the rate of a reaction is to increase its temperature . When you heat a substance . its particles move faster . particles increase the tion rate in two ways . First . the particles come in contact more often , which means there are more chances tor at reaction to happen . Second . particles have more energy . This increased energy causes more particles of the reactants to get over the activation In contrast . reducing temperature slows down reaction rates . For example . milk contains bacteria , which carry out thousands of chemical reactions as they live and reproduce . At room temperature . those reactions happen faster and milk spoils more quickly . You store and other foods in the refrigerator because keeping foods cold slows down those tions . so your foods stay fresh longer . Concentration A third way to increase the rate of a cal reaction is to increase the concentration of the reactants . Concentration is the amount of a substance in a given volume . For example . adding small spoonful of sugar to a glass of will make it sweet . But adding a large spoonful of sugar makes the lemonade sweeter . The glass with more sugar has a greater concentration of sugar molecules . Increasing the concentration of reactants supplies more particles to react . Compare the two reactions of acid and metal in Figure IS . The test tube on the left has at lower concentration of acid . This reaction is slower than the one on the right . where the acid concentration is higher . You see ior the increased rate of reaction in the greater amount of gas bubbles produced . daunting why my an Increase In temperature affect the ' of chemical ?

Another way to control the rate of a reaction is to change the activation energy needed . A ( KAT uh list ) is a material that increases the rate of a reaction by lowering the activation energy . Although catalysts affect a reaction rate . they are not changed by a reaction . For this reason catalysts are not considered reactants . Many chemical reactions happen at temperatures that would kill living things Yet . some of these reactions are for life . The cells in ( as in all living things ) tain biological catalysts called enzymes EN ) body has thousands of different enzymes . Each one is om , affects only one chemical reaction . As shown in Figure provide a surface on which reactions can take place . By bringing reactant molecules close together , the enzyme lowers the activation energy needed . In this way . enzymes make chemical reactions that are necessary for life happen at a low temperature . Inhibitors Sometimes a is more useful when it can be , slowed down rather than up . A material used to enzyme decrease the rate of a reaction is an inhibitor . Most inhibitors 9998 ' work by preventing reactants from coming together . Usually flaunt 16 they combine with one of the reactants either permanently or temporarily . Inhibitors include preservatives added to food products to prevent them from becoming stale or spoiling . After a reaction . on enzyme molecule is unchanged . Section Assessment Target Reading Skill Take Notes Review your notes for this are two main ideas that you noted concerning rates of chemical reactions ?

Reviewing Key Concepts if . I . Defining What is activation energy ?

Comparing Reaction Rates Place an iron nail in a plastic ( up . Add enough water to almost cover the I . Describing What role docs activation energy play in , Mam a ma , of fine . steel wool in another cup and add El . Making Generalizations Look at the diagram the um , amount of wan Ask Figure , and make a generalization about activation media energy in and endothermic reactions . will happen overnight . The next . Identifying What are four ways that chemists can my , amen , control the rates of chemical reactions ?

of rust . Applying Concepts Which would react more quickly on each . were your family in at chemical reaction a single sugar or an equal predictions correct ?

Explain how mass of granulated sugar crystals ?

Explain . surface areas affect reaction rates . chapters can Temperature and Enzyme Activity 223 . Problem Hydrogen peroxide is a poisonous waste product of reactions in living things . Catalase is an enzyme that speeds up the breakdown of gen peroxide Into water and oxygen gas . does temperature affect the action of the enzyme ?

Skills Focus calculating , graphing , interpreting data , drawing conclusions Materials forceps stopwatch test tube with a stopper hydrogen peroxide solution filter paper disks soaked in liver preparation enzyme ) and kept at four different temperatures ( room temperature , and ) container to hold water ( or bowl ) Write a hypothesis explaining how the action of the enzyme is related to temperature . Auk your teacher lor the room . MO . Make a data table like the one below . Get the room temperature from your teacher . Fill a container with water . Then fill a test tube with hydrogen peroxide solution until the test tube is overflowing . Do this over a sink or the container of water . the small end of a stopper with water . Using forceps , remove a filter paper disk soaked in liver preparation ( catalase ) that has been kept at room temperature . Stick it to the moistened end of the stopper . Your partner should be ready with the stopwatch tor the next step . Place the stopper firmly into the test tube . hold your thumb over the hole . and quietly invert the test tube . Start the stopwatch . Put the inverted end of the test tube into the container of water . as shown in the graph , and remove your thumb .

This test tube shows the vigorous reaction that occurs between gen peroxide and catalase that is found in the blood . lfthe hydrogen peroxide breaks down , oxygen will be produced . Oxygen bubbles will cling to the disk and cause it to float . Record the time it takes for the disk to rise to the top . If the disk does not rise within 30 seconds . record no tion and go on to Step . Rinse the test tube and repeat the procedure with catalase enzyme disks kept at , 37 , and 100 . CAUTION When you remove the disk kept in the hot water bath , do not use your bare hands . Avoid . Drawing Conclusions What can you conclude about the activity of the enzyme at the various temperatures you tested ?

Hint Enzyme activity is greater when the rate of reaction is faster . Predicting Make a prediction about how active the enzyme would be at 10 , 60 , and . Give reasons to support your prediction . Communicating A buildup of gen peroxide in living things can damage cells . The normal human body temperature is 37 Write a ' paragraph relating your results to th bod st tur rid its ed conclude . Calculating Calculate the average time for each temperature based on the results of the entire class . Enter the results in your data table . Graphing Make a line graph of the data you collected . Label the axis ( Temperature with a scale lrom to 100 label the vertical axis ( Time with different enzyme concentrations . a scale from to 30 seconds . Plat Obtain your teachers permission before the class average time tor each carrying out your investigation , temperature . Interpreting Data What evidence do you have that your hypothesis from Step is either supported or not Design an Experiment The activity oi an enzyme also depends upon the concentration of the enzyme . Design an experiment that explores the relationship between enzyme activity and enzyme concentration . Your can give you disks soaked with supported ?

Interpreting Data Now is the time it takes the disk to rise to the top oi the inverted tube related to the rate Vi ' of the reaction ?

Mon out , Students know ( al reactions usually heat or absorb heat . What are the three things necessary to maintain a fun Why should you know about the causes of tire and how to prevent a tire ?

Key Terms combustion I Firefighters battle a blaze . Fire and Fire Safety How Does Baking Soda Affect a Fire ?

Put on your safety goggles . Secure a small candle in a holder or a ball of clay . Alter instructions from your teacher , use a match to light the candle . Place a beaker next to the candle . Measure large of baking soda into the beaker . Add about 100 of water and Stir . Add about 100 of vinegar . As soon as the mixture stops foaming , tip the beaker as if you are pouring something out of it onto the flame . CAUTION Do not pour any liquid on the candle . Observe what happens to the flame . Think It Over Developing Hypotheses The gas produced in the beaker was carbon dioxide , Based on the results of this experiment , develop a hypothesis to explain what you observed Ifl Step . The all in . Fin ! A blue has been spotted in wan . aboard the ladder truck and the hose truck . Lights . sirens ' and ' a path for the trucks . Tits from their training that is a ( tion that can be only if reach it in time .

Understanding Fire Fire is the result of combustion , a rapid reaction between oxygen and a Fuel . A fuel is a material that releases energy when it burns . Common fuels include oil , wood , gasoline , natural gas . and paper . of these types of fuel always produces carbon dioxide and water . When fuels don ! burn completely . products such as smoke and poisonous gases may be produced . The Fire Triangle Although a combustion reaction is very exothermic and fast , can not start unless conditions are right . things necessary to start and maintain I lire are fuel . oxygen , and heat . You probably know that oxygen is one of the gases in air . About 20 percent ol the air around you is posed of oxygen gas . If air can reach the fuel . so can oxygen . A large can create a strong draft that pulls air toward it . As the air around the is heated . it rises rapidly . Cooler air toward the fire , replace ing the heated air and bringing a fresh supply of if you stand in front of a tire in a . you can feel the air toward the tire . Heat is a part of the triangle . Fuel and oxygen can be together , but they won ! until something provides the activation energy to start combustion . This energy can come from a lighted match . an electric spark . or the heat from a stove . Once combustion starts . the heat released supplies more activation energy to keep the reaction going . Once started . a tire can continue burning as long as all components of the tire triangle are available . Coal in abandoned mines under the town of , started burning iu 1962 . The coal is still burn ing . Many old lead into the tunnels . Because some can not be located and sealed , air ties to flow into the mines . supporting the tire . Heat and poisonous gases coming up from the lire through cracks in the ground made living in . Everyone eventually moved away . No one knows how long this will continue to burn . What is heat role in starting a live ?

Fawn 17 The Fire Triangle The tire triangle can be controlled in the grill below . if any point of the fire triangle is missing . a fire will not continue . Applying Concepts How would closing the lower air vents affect the fire ?

Escaping gases om Controlling Fire Use your knowledge of chemical reactions GO to think of ways to control fire . What if you remove one pan cy , of the fire triangle ?

For example . you can get the fuel away ' from the . You can also keep oxygen from getting to the fuel . Finally . you can cool the combustion reaction . How do usually ?

They use hoses to spray huge amounts of water on the flames . Water removes two parts of the fire triangle . First , water covers the fuel , which keeps it from coming into contact with oxygen . Second . ration of the water uses a large amount of heat , causing the tire to cool . Without heat . there is enough energy to continue the combustion . Therefore . the reaction stops . Home Fire Safety Every year , claims thousands of lives in the United States . lfyou know how to prevent tires in your home and what . You may save your home or even your life ! The most common sources of home are small heaters . cooking . and faulty electrical wiring . The tires that cause the most deaths start from carelessness with cigarettes . for . Links on fire solely Visit Web Code Fighting Fires You can light a small lire by using what you know about the tire triangle . For example . carbon dioxide gas can smother a by preventing contact between the fuel and oxygen in the air . Therefore . you can put out a small on the stove by throwing baking soda on it . Baking soda decomposes when heated and releases carbon dioxide gas . Or . you can use the cover of a saucepan to cut oil the of oxygen . Smoke 537 ! ladder Matches out at smoke A House This house has marry and fire safety ' We futures . Why are phone ' smoke detectors located on numbers every ?

Water heater A small tire is easy to control . You can cool a match enough to stop combustion just by blowing on it . A small in a trash can may be doused with a pan of water . if the tire spreads to the curtains . however , even garden hose might not deliver enough water to put it out . One most effective ways to a small fire is with a tire extinguisher . But at tin that is growing as you light it is out of control . if a tire is out , there is only one safe thing to away from the and call the department . Preventing The best form of tire satiety is tion . 18 shows some features of a house . You can also check your home to he sure that all items are stored safely away from sources of . such as the kitchen stove . Fires can be dangerous and deadly , but many fires can be prevented it you are careful . Understanding the chemistry of tire gives you it way to risk and increase your safety . Now does baking soda put a tin out ! 19 Fire extinguishers and baking soda can be wed to interrupt the fire triangle . Smoke detectors can help you identify a fire and escape to safety . Assessment Section Target Reading Skill Yoko Notes Review your notes for this section . What important details you include about preventing tires in your home ?

Reviewing Key Concepts I . a . Listing What three things are required for combustion ?

Explaining the triangle help you control EU lire ?

in I Applying Concepts To stop a forest lire . may remove all the trees in a strip ofland that lies in the path of the part of the lure triangle is ?

Explain . I . Reviewing Why is it important to know about the causes of and how to prevent ?

I What are the three most common causes of home ?

Problem Solving Choose one common cause of home . Describe measures that can he taken to prevent Fires of this type . 565 Family Plan Work with your family to formulate a fire safety plan . How can tires be prevented in your home ?

How can tires be put out if they occur ?

is there a functioning smoke detector on each floor at the home , especially near the bedrooms ?

How can the fire department be contacted in an emergency ?

Design a fire escape route . Make sure all family members know the route as well as a meeting place outside . ous imam Study Guide are In atoms are rearranged into different of molecules . 71 Observing Chemical Change Key Concepts , in matter can be in terms ni i and chemical . mi ( when bonds break and new bonds form . in And in energy you can . Key Terms nutter product ' endothermic . uh change Chem al Reactions Key Concepts Chemical inc chemical formulas and ' In . In . number in . ys nu how they an , so their total , stays the . Tu I ( au . chemical mun show Ih of type on both side the . Three general types , and replacement . Key Terms equation ' of matter system replacement 2460 controlling Chemical Reactions Key . of energy to get that rates of ( and the premier ut catalysts ur . Key Terms activation inhibitor Fire and Fire Safety Key Concepts Thu arc ) Io start and maintain oxygen , and heat . know how In in home and what to do It . you are better In lake , Key terms combustion fuel

Far . Visit Web Code Review and Assessment Reading Skill Take Notes In your . create it two column not Recall Clues and Questions What are chemical equations ?

Mates equation an easy way to show a chemical reaction , Chemical for Chemical . Include ) elements in I compound Structure of an Reviewing Key Terms ( house the letter of the best answer . Which of the is not Complete the following sentences so that your answers clearly explain the key terms . A burning is an example ofit chemical mu , Chang in which . The left side of equation lists the ' I IlS , ur sub ability In I I . By the and ( HINT . ill ' products of at . you can i bi the ul conservation of matter . A ( a . which , changes . 10 . Our actor that can rates 13 a I . nun . You can ) by , changing . A ) in which two HINT . to form at compound called . replacement . Ig ( i You are a writer ( or a I he energy chemical reaction bug about chemistry . paragraph that a . 15 by a young children would understand that at th end . explains the concept of activation ( A thy , Be sure to use examples , such as the burning with . Wood 935 . reaction in which , with ) at in . I ( reaction . Chemical Reactions , rse a

Review and Assessment Checking Concepts 11 . are the two kinds of change that occur in ?

yuu tan tell rune the other . 12 . Why an ! Il ( the at the reactant the ?

13 . You the truss of piece of tron metal , let it rust . and again . I mass has . Ill ( I ' How do ) make reactions occur at safe ?

Why dues on a help tu put the um ?

16 . useful in controlling ?

Thin 17 . Problem Solving Steel that is to water and uh rusts . If you were a , huw you rich ?

why yuur works . Crit ally 18 . Classifying The for ' vault of ( is , or . a . 19 . Relating Cause and Effect open doors wry carefully because will violently when the is on your of the fur . explain why this . 20 . Some statue art nude that can react itt arid ruin begin In . It has been observed that statues with an by Acid rain much than statues with very ( 2480 Math Practice Balance the chemical in Questions . 21 . 11 . 03 23 . 24 . Fe ( Applying Skills Use the energy diagram to answer Questions . two smite ' 25 . Data Hun dues thu products compare with the ?

26 . this reaction or . 27 . Applying Concepts What change in might fut the hump in the second graph ?

Explain . Standards Investigation Performance Assessment Make at of your test . class , how your was built to the ! hy the class . its safety features . Based un your . rate how ' as it ) IL Standards Practice Choose the letter at the best answer . Which ofthe following is the best evidence for a chemical reaction ?

A gas bubbles ofa new substance change change in temperature . Which statement best describes what happens to chemical bonds in a reaction ?

A Bonds are only broken . not formed I Bonds are only formed . not . Bonds in the reactants are broken . and bonds in the products are formed . Bonds are neither nor broken , Which shows at balanced chemical equation for the decomposition of aluminum , A 03 I ZAI 303 , Argo , Al 30 , Use the diagram below to answer Question . Reaction . The quantity ( in the diagram the A activation energy ofthe reaction . I energy absorbed by the reaction . energy released by the . temperature of the reactants . at use your answers to Questions and on the diagram below . The diagram represents molecules of two different elements that are gases . The elements react chemically to produce a third gas . The diagram represents at ) A endothermic reaction in which energy is released . I exothermic reaction in which energy is absorbed . exothermic in which energy is . in which energy is destroyed . What can be inferred from the diagram ?

A Matter is not created or destroyed in a chemical reaction . I The rate of a reaction depends on the surface area of the reactants . A gas molecule always consists of two identical atoms . The product is carbon gas . The major component natural gas is methane tCH , When methane burns in oxygen gas ) carbon dioxide ( and vapor ( are produced . Write a balanced equation for this reaction . Explain why the burning of methane is a chemical change , not a physical change . Does this change absorb heat or liberate heat ?

15 chapters us