Chemical Reactions - Mr. Mesic's Science Classes€¦ · visible clues that sugar molecules ... You...

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ChemicalReactions

What chemical reactions happen at chemical plants?Chemical plants like this one provide the starting materials forthousands of chemical reactions. The compact discs you listen to,personal items, such as shampoo and body lotion, and medicines allhave their beginnings in a chemical plant.

What additional types of products do you think are manufacturedin a chemical plant?Science Journal

In chemical reactions, atoms in reactants arerearranged to form products with differentchemical properties.

SECTION 1Chemical Formulas and EquationsMain Idea Atoms are notcreated or destroyed inchemical reactions—theyare just rearranged.

SECTION 2Rates of ChemicalReactionsMain Idea Reaction rates are affected by several things, includingtemperature, concentration,surface area, inhibitors, and catalysts.

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Start-Up Activities

Chemical Reaction Make thefollowing Foldable to help youunderstand chemical reactions.

Fold a verticalsheet of notebook paper in halflengthwise.

Cut along every third line of only thetop layer to form tabs.

Label each tab.

Research Information Before you read thechapter, write several questions you haveabout chemical reactions on the front of thetabs. As you read, add more questions. Underthe tabs of your Foldable, write answers to thequestions you recorded on the tabs.

STEP 3

STEP 2

STEP 1

Preview this chapter’s contentand activities at bookl.msscience.com

Identify a Chemical ReactionYou can see substances changing every day.Fuels burn, giving energy to cars and trucks.Green plants convert carbon dioxide andwater into oxygen and sugar. Cooking an egg or baking bread causes changes too.These changes are called chemical reactions.In this lab you will observe a common chemi-cal change.WARNING: Do not touch the test tube. It willbe hot. Use extreme caution around an openflame. Point test tubes away from you andothers.

1. Place 3 g of sugar into a large test tube.

2. Carefully light a laboratory burner.

3. Using a test-tube holder, hold the bottomof the test tube just above the flame for45 s or until something happens with thesugar.

4. Observe any change that occurs.

5. Think Critically Describe in your ScienceJournal the changes that took place in thetest tube. What do you think happened tothe sugar? Was the substance thatremained in the test tube after heating thesame as the substance you started with?

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36 A ◆ L CHAPTER 2 Chemical Reactions

Apply It! Before you read, skimthe questions in the Chapter Review. Choosethree questions and predict the answers.

Learn It! A prediction is an educated guess based on whatyou already know. One way to predict while reading is to guess what youbelieve the author will tell you next. As you are reading, each new topicshould make sense because it is related to the previous paragraph or passage.

Practice It! Read the excerpt below from Section 1.Based on what you have read, make predictions about what you will read in the rest of the lesson. After you read Section 1, go back to your predictions to see if they were correct.

Matter can undergo two kinds ofchanges—physical and chemical. Physicalchanges in a substance affect only the physicalproperties, such as size and shape, or whetherit is a solid, liquid, or gas. For example, whenwater freezes, its physical state changes fromliquid to solid, but it is still water.

—from page 36

Predict what typeof propertieschemical changesaffect.

Do you thinkmelting is a chemical or physical change?

Predict whatmight happen tothe atoms inwater when itundergoes achemical change.

L ◆ 36 B

Before You Read Statement After You ReadA or D A or D

1 Burning is an example of a chemical change.

2 A chemical equation only tells the names ofreactants and products.

3 When a substance burns, atoms disappear andnew atoms are created.

4 When balancing a chemical equation, it’s okayto change the subscripts of a chemical formula.

5 Some reactions release energy and some adsorbenergy.

6 During chemical reactions, bonds in the reactantsbreak and new bonds form.

7 Reactions that release energy do not need anyenergy to start the reaction.

8 Increasing temperature will speed up mostchemical reactions.

Print out a worksheetof this page at bookl.msscience.com

As you read, check the

predictions you made to see if

they were correct.Use this to focus on the main ideas as you read the chapter.

Before you read the chapter, respond to the statements

below on your worksheet or on a numbered sheet of paper.

• Write an A if you agree with the statement.

• Write a D if you disagree with the statement.

After you read the chapter, look back to this page to see if you’ve

changed your mind about any of the statements.

• If any of your answers changed, explain why.

• Change any false statements into true statements.

• Use your revised statements as a study guide.


36 ◆ L CHAPTER 2 Chemical Reactions

Physical or Chemical Change?You can smell a rotten egg and see the smoke from a campfire.

Signs like these tell you that a chemical reaction is taking place.Other evidence might be less obvious, but clues are always presentto announce that a reaction is under way.

Matter can undergo two kinds of changes—physical andchemical. Physical changes in a substance affect only physicalproperties, such as its size and shape, or whether it is a solid,liquid, or gas. For example, when water freezes, its physical statechanges from liquid to solid, but it’s still water.

In contrast, chemical changes produce new substances thathave properties different from those of the original substances.The rust on a bike’s handlebars, for example, has properties different from those of the metal around it. Another example isthe combination of two liquids that produce a precipitate, whichis a solid, and a liquid. The reaction of silver nitrate and sodiumchloride forms solid silver chloride and liquid sodium nitrate. Aprocess that produces chemical change is a chemical reaction.

To compare physical and chemical changes, look at thenewspaper shown in Figure 1. If you fold it, you change its sizeand shape, but it is still newspaper. Folding is a physical change.If you use it to start a fire, it will burn. Burning is a chemicalchange because new substances result. How can you recognize achemical change? Figure 2 shows what to look for.

Chemical Formulasand Equations

■ Determine whether or not a chemical reaction is occurring.

■ Determine how to read and understand a balanced chemicalequation.

■ Examine some reactions thatrelease energy and others thatabsorb energy.

■ Explain the law of conservationof mass.

Chemical reactions warm yourhome, cook your meals, digest yourfood, and power cars and trucks.

Review Vocabularyatom: the smallest piece of mat-ter that still retains the propertyof the element

New Vocabulary

• chemical reaction

• reactant

• product

• chemical equation

• endothermic reaction

• exothermic reaction

Figure 1 Newspaper can undergo bothphysical and chemical changes.

Physical change

Chemical change

(l)Aaron Haupt, (r)Doug Martin

NGS TITLE

Figure 2

VISUALIZING CHEMICAL REACTIONS

Chemical reactions take place when chemicals combine toform new substances. Your senses—sight, taste, hearing,smell, and touch—can help you detect chemical reactionsin your environment.

TASTE A boy grimacesafter sipping milk that has gone sour due to a chemical reaction.

HEARING A Russian cos-monaut hoists a flare into theair after landing in the oceanduring a training exercise. Thehissing sound of the burningflare is the result of a chemi-cal reaction.

SMELL AND TOUCH Billowing clouds of acrid smoke and waves ofintense heat indicate that chemical reactions are taking place in thisburning forest.

SIGHT When you spot a firefly’s bright glow, you are seeing a chemicalreaction in progress—two chemicals are combining in the firefly’s abdo-men and releasing light in the process. The holes in a slice of bread are visible clues that sugar molecules were broken down by yeast cells in achemical reaction that produces carbon dioxide gas. The gas caused thebread dough to rise.

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SECTION 1 Chemical Formulas and Equations L ◆ 37(tl)Patricia Lanza, (tc)Jeff J. Daly/Visuals Unlimited, (tr)Susan T. McElhinney, (bl)Craig Fuji/Seattle Times, (br)Sovfoto/Eastfoto/PictureQuest


Chemical EquationsTo describe a chemical reaction, you must know which sub-

stances react and which substances are formed in the reaction.The substances that react are called the reactants (ree AK tunts).Reactants are the substances that exist before the reactionbegins. The substances that form as a result of the reaction arecalled the products.

When you mix baking soda and vinegar, a vigorous chemi-cal reaction occurs. The mixture bubbles and foams up insidethe container, as you can see in Figure 3.

Baking soda and vinegar are the common names for thereactants in this reaction, but they also have chemical names.Baking soda is the compound sodium hydrogen carbonate(often called sodium bicarbonate), and vinegar is a solution ofacetic (uh SEE tihk) acid in water. What are the products? Yousaw bubbles form when the reaction occurred, but is thatenough of a description?

Describing What Happens Bubbles tell you that a gas hasbeen produced, but they don’t tell you what kind of gas. Arebubbles of gas the only product, or do some atoms from thevinegar and baking soda form something else? What goes on inthe chemical reaction can be more than what you see with youreyes. Chemists try to find out which reactants are used andwhich products are formed in a chemical reaction. Then, theycan write it in a shorthand form called a chemical equation.A chemical equation tells chemists at a glance the reactants,products, and proportions of each substance present. Someequations also tell the physical state of each substance.

What does a chemical equation tell chemists?

Figure 3 The bubbles tell youthat a chemical reaction has takenplace.Predict how you might find outwhether a new substance hasformed.

Amanita Pictures

SECTION 1 Chemical Formulas and Equations L ◆ 39

Using Words One way you can describe a chemical reactionis with an equation that uses words to name the reactants andproducts. The reactants are listed on the left side of an arrow,separated from each other by plus signs. The products are placedon the right side of the arrow, also separated by plus signs. Thearrow between the reactants and products represents thechanges that occur during the chemical reaction. When readingthe equation, the arrow is read as produces.

You can begin to think of processes as chemical reactions evenif you do not know the names of all the substances involved.Table 1 can help you begin to think like a chemist. It shows theword equations for chemical reactions you might see around yourhome. See how many other reactions you can find. Look for thesigns you have learned that indicate a reaction might be takingplace. Then, try to write them in the form shown in the table.

Using Chemical Names Many chemicals used around thehome have common names. For example, acetic acid dissolvedin water is called vinegar. Some chemicals, such as baking soda,have two common names—it also is known as sodium bicar-bonate. However, chemical names are usually used in wordequations instead of common names. In the baking soda andvinegar reaction, you already know the chemical names of thereactants—sodium hydrogen carbonate and acetic acid. Thenames of the products are sodium acetate, water, and carbondioxide. The word equation for the reaction is as follows.

Acetic acid � Sodium hydrogen carbonate →Sodium acetate � Water � Carbon dioxide

Autumn Leaves A colorchange can indicate achemical reaction. Whenleaves change colors inautumn, the reaction maynot be what you expect.The bright yellow andorange are always in theleaves, but masked bygreen chlorophyll. Whenthe growth season ends,more chlorophyll is brok-en down than produced.The orange and yellowcolors become visible.

Table 1 Reactions Around the Home

Reactants Products

Baking soda + Vinegar → Gas + White solid

Charcoal + Oxygen → Ash + Gas +Heat

Iron + Oxygen + Water → Rust

Silver + Hydrogen sulfide → Black tarnish + Gas

Gas (kitchen range) + Oxygen → Gas + Heat

Sliced apple + Oxygen → Apple turns brown

Using Formulas The word equation for the reaction of bak-ing soda and vinegar is long. That’s why chemists use chemicalformulas to represent the chemical names of substances in theequation. You can convert a word equation into a chemicalequation by substituting chemical formulas for the chemicalnames. For example, the chemical equation for the reactionbetween baking soda and vinegar can be written as follows:

Subscripts When you look at chemical formulas, notice thesmall numbers written to the right of the atoms. These numbers,called subscripts, tell you the number of atoms of each element inthat compound. For example, the subscript 2 in CO2 means thateach molecule of carbon dioxide has two oxygen atoms. If an atomhas no subscript, it means that only one atom of that element is inthe compound, so carbon dioxide has only one carbon atom.

Conservation of Mass What happens to the atoms in the reactants when they are con-

verted into products? According to the law of conservation of mass,the mass of the products must be the same as the mass of the reac-tants in that chemical reaction. This principle was first stated by theFrench chemist Antoine Lavoisier (1743–1794), who is consideredthe first modern chemist. Lavoisier used logic and scientific meth-

ods to study chemical reactions. Heproved by his experiments that nothingis lost or created in chemical reactions.

He showed that chemical reactionsare much like mathematical equa-tions. In math equations, the right andleft sides of the equation are numeri-cally equal. Chemical equations aresimilar, but it is the number and kindof atoms that are equal on the twosides. Every atom that appears on thereactant side of the equation alsoappears on the product side, as shownin Figure 4. Atoms are never lost orcreated in a chemical reaction; how-ever, they do change partners.

CH3COOH � NaHCO3 → CH3COONa � H2O � CO2

Acetic Sodium Sodium Water Carbonacid hydrogen acetate dioxide

(vinegar) carbonate(baking soda)

Observing the Law ofConservation of Mass Procedure1. Place a piece of steel wool

into a medium test tube.Seal the end of the testtube with a balloon.

2. Find the mass.3. Using a test-tube holder,

heat the bottom of thetube for two minutes in ahot water bath providedby your teacher. Allow thetube to cool completely.

4. Find the mass again.

Analysis 1. What did you observe that

showed a chemical reac-tion took place?

2. Compare the mass beforeand after the reaction.

3. Why was it important forthe test tube to be sealed?

CH3COOH + NaHCO3 CH3COONa + H2O + CO2

Na

H

H C

CC

O

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H

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NaC

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Reactants Products

Figure 4 The law of conserva-tion of mass states that the num-ber and kind of atoms must beequal for products and reactants.


SECTION 1 Chemical Formulas and Equations L ◆ 41

Balancing Chemical Equations When you write the chemical equation for a reaction, you

must observe the law of conservation of mass. Look back atFigure 4. It shows that when you count the number of carbon,hydrogen, oxygen, and sodium atoms on each side of the arrowin the equation, you find equal numbers of each kind of atom.This means the equation is balanced and the law of conservationof mass is observed.

Not all chemical equations are balanced so easily. For exam-ple, silver tarnishes, as in Figure 5, when it reacts with sulfurcompounds in the air, such as hydrogen sulfide. The followingunbalanced equation shows what happens when silver tarnishes.

Count the Atoms Count the number of atoms of each typein the reactants and in the products. The same numbers ofhydrogen and sulfur atoms are on each side, but one silver atomis on the reactant side and two silver atoms are on the productside. This cannot be true. A chemical reaction cannot create a sil-ver atom, so this equation does not represent the reaction cor-rectly. Place a 2 in front of the reactant Ag and check to see if theequation is balanced. Recount the number of atoms of each type.

The equation is now balanced. There are an equal number ofsilver atoms in the reactants and the products. When balancingchemical equations, numbers are placed before the formulas as youdid for Ag. These are called coefficients. However, never change thesubscripts written to the right of the atoms in a formula. Changingthese numbers changes the identity of the compound.

2Ag � H2S → Ag2S � H2

Ag � H2S → Ag2S � H2

Silver Hydrogen Silver Hydrogensulfide sulfide

Figure 5 Keeping silverbright takes frequent polishing,especially in homes heated bygas. Sulfur compounds found insmall concentrations in naturalgas react with silver, formingblack silver sulfide, Ag2S.

2Ag � H2S 0 Ag2S � H2

Hydrogen(H2)

Silver(Ag)

Silversulfide(Ag2S)

Hydrogen sulfide (H2S)

Topic: Chemical EquationsVisit for Weblinks to information about chemicalequations and balancing them.

Activity Find a chemical reac-tion that takes place around yourhome or school. Write a chemicalequation describing it.

bookl.msscience.com

Sovfoto/Eastfoto/PictureQuest


Energy in Chemical ReactionsOften, energy is released or absorbed during a chemical reac-

tion. The energy for the welding torch in Figure 6 is releasedwhen hydrogen and oxygen combine to form water.

Energy Released Where does this energy come from? Toanswer this question, think about the chemical bonds that breakand form when atoms gain, lose, or share electrons. When sucha reaction takes place, bonds break in the reactants and newbonds form in the products. In reactions that release energy, theproducts are more stable, and their bonds have less energy thanthose of the reactants. The extra energy is released in variousforms—light, sound, and thermal energy.

2H2 � O2 → 2H2O � energy

Balancing Equations

CONSERVING MASS Methane and oxygen react to form carbon dioxide and water. You cansee how mass is conserved by balancing the equation: CH4 � O2 → CO2 � H2O.

SolutionThis is what you know:

The number of atoms of C, H, and O in reactants and products.

This is what you need to do:

Make sure that the reactants and products have equal numbers of atoms of each element. Start with the reactant having the greatest number of different elements.

Reactants Products Action

CH4 � O2 CO2 � H2O Need 2 more H atoms in Productshave 4 H atoms have 2 H atoms Multiply H2O by 2 to give 4 H atoms

CH4 � O2 CO2 � 2H2O Need 2 more O atoms in Reactantshave 2 O atoms have 4 O atoms Multiply O2 by 2 to give 4 O atoms

The balanced equation is CH4 � 2O2 → CO2 � 2H2O.

Check your answer:

Count the carbons, hydrogens, and oxygens on each side.

1. Balance the equation Fe2O3 � CO → Fe3O4 � CO2.

2. Balance the equation Al � I2 → AlI3.


For more practice, visit bookl.msscience.com/math_practice


Figure 6 This welding torchburns hydrogen and oxygen toproduce temperatures above3,000°C. It can even be usedunderwater. Identify the products of this chemical reaction.

Figure 7 Electrical energy isneeded to break water into itscomponents. This is the reverse ofthe reaction that takes place in thewelding torch shown in Figure 6.

Energy Absorbed What happens when the reverse situationoccurs? In reactions that absorb energy, the reactants are more sta-ble, and their bonds have less energy than those of the products.

In this reaction the extra energy needed to form the productscan be supplied in the form of electricity, as shown in Figure 7.

Reactions can release or absorb several kinds of energy, includ-ing electricity, light, sound, and thermal energy. When thermalenergy is gained or lost in reactions, special terms are used.Endothermic (en doh THUR mihk) reactions absorb thermalenergy. Exothermic (ek soh THUR mihk) reactions releasethermal energy. The root word therm refers to heat, as it doesin thermos bottles and thermometers.

Energy Released Several types of reactions that release ther-mal energy. Burning is an exothermic chemical reaction inwhich a substance combines with oxygento produce thermal energy along withlight, carbon dioxide, and water.

What type of chemicalreaction is burning?

Rapid Release Sometimes energy isreleased rapidly. For example, charcoallighter fluid combines with oxygen in theair and produces enough thermal energy toignite a charcoal fire within a few minutes.

2H2O � energy → 2H2 � O2

Water Hydrogen Oxygen

Electrical energyfrom a battery

Hydrogen (H2)

Oxygen (O2)

Water (H2O)

SECTION 1 Chemical Formulas and Equations L ◆ 43Christopher Swann/Peter Arnold, Inc.


Figure 8 Two exothermicreactions are shown.The charcoal fire tocook the food wasstarted whenlighter fluidcombined rap-idly with oxy-gen in air. Theiron in thewheelbarrowcombinedslowly with oxy-gen in the air toform rust.

Fast reaction

Slow Release Other materials also combine withoxygen but release thermal energy so slowly that you

cannot see or feel it happen. This is the case when ironcombines with oxygen in the air to form rust. The slow

release of thermal energy from a reaction also is used in heatpacks that can keep your hands warm for several hours. Fast andslow energy release are compared in Figure 8.

Energy Absorbed Some chemical reactions and physicalprocesses need to have thermal energy added before they canproceed. An example of an endothermic physical process thatabsorbs thermal energy is the cold pack shown in Figure 9.

The heavy plastic cold pack holds ammonium nitrate andwater. The two substances are separated by a plastic divider.When you squeeze the bag, you break the divider so that theammonium nitrate dissolves in the water. The dissolving processabsorbs thermal energy, which must come from the surroundingenvironment—the surrounding air or your skin after you placethe pack on the injury.

Figure 9 The thermal energyneeded to dissolve the ammoniumnitrate in this cold pack comesfrom the surrounding environment.

Slow reaction

(tl)Frank Balthis, (tr)Lois Ellen Frank/CORBIS, (b)Matt Meadows

Self Check1. Determine if each of these equations is balanced. Why

or why not?

a. Ca � Cl2 → CaCl2b. Zn � Ag2S → ZnS � Ag

2. Describe what evidence might tell you that a chemical reaction has occurred.

3. Think Critically After a fire, the ashes have less massand take up less space than the trees and vegetationbefore the fire. How can this be explained in terms ofthe law of conservation of mass?

SummaryPhysical or Chemical Change?

• Matter can undergo physical and chemicalchanges.

• A chemical reaction produces chemicalchanges.

Chemical Equations

• A chemical equation describes a chemicalreaction.

• Chemical formulas represent chemical namesfor substances.

• A balanced chemical equation has the samenumber of atoms of each kind on both sidesof the equation.

Energy in Chemical Reactions

• Endothermic reactions absorb thermal energy.

• Exothermic reactions release thermal energy.

4. Calculate The equation for the decomposition of silver oxide is 2Ag2O → 4Ag � O2. Set up a ratio tocalculate the number of oxygen molecules releasedwhen 1 g of silver oxide is broken down. There are 2.6 � 1021 molecules in 1 g of silver oxide.

Energy in the Equation The wordenergy often is written in equations as eithera reactant or a product. Energy written as areactant helps you think of energy as a nec-essary ingredient for the reaction to takeplace. For example, electrical energy isneeded to break up water into hydrogen andoxygen. It is important to know that energymust be added to make this reaction occur.

Similarly, in the equation for an exother-mic reaction, the word energy often is writtenalong with the products. This tells you thatenergy is released. You include energy when writing the reactionthat takes place between oxygen and methane in natural gas whenyou cook on a gas range, as shown in Figure 10. This thermalenergy cooks your food.

Although it is not necessary, writing the word energy candraw attention to an important aspect of the equation.

CH4 � 2O2 → CO2 � 2H2O � energy

Methane Oxygen Carbon Water dioxide

Figure 10 Energy from a chem-ical reaction is used to cook.Determine if energy is used as a reactant or a product in this reaction.

bookl.msscience.com/self_check_quiz SECTION 1 Chemical Formulas and Equations L ◆ 45David Young-Wolff/PhotoEdit/PictureQuest



How Fast? Fireworks explode in rapid succession on a summer night.

Old copper pennies darken slowly while they lie forgotten in adrawer. Cooking an egg for two minutes instead of five min-utes makes a difference in the firmness of the yolk. Theamount of time you leave coloring solution on your hair mustbe timed accurately to give the color you want. Chemical reac-tions are common in your life. However, notice from theseexamples that time has something to do with many of them. Asyou can see in Figure 11, not all chemical reactions take placeat the same rate.

Some reactions, such as fireworks or lighting a campfire,need help to get going. You may also notice that others seem tostart on their own. In this section, you will also learn about fac-tors that make reactions speed up or slow down once they getgoing.

Rates of Chemical Reactions

■ Determine how to describe andmeasure the speed of a chemicalreaction.

■ Identify how chemical reactionscan be sped up or slowed down.

Speeding up useful reactions andslowing down destructive ones canbe helpful.

Review Vocabularystate of matter: physical prop-erty that is dependent on temper-ature and pressure and occurs infour forms—solid, liquid, gas, orplasma

New Vocabulary

• activation energy

• rate of reaction

• concentration

• inhibitor

• catalyst

• enzyme

Figure 11 Reaction speeds vary greatly.Fireworks are over in a few seconds. However, thecopper coating on pennies darkens slowly as itreacts with substances it touches.

(l)Amanita Pictures, (r)Richard Megna/Fundamental Photographs/Photo Researchers

SECTION 2 Rates of Chemical Reactions L ◆ 47

Activation Energy—Starting a ReactionBefore a reaction can start, molecules of the reactants have to

bump into each other, or collide. This makes sense because toform new chemical bonds, atoms have to be close together. But,not just any collision will do. The collision must be strongenough. This means the reactants must smash into each otherwith a certain amount of energy. Anything less, and the reactionwill not occur. Why is this true?

To form new bonds in the product, old bonds must break inthe reactants, and breaking bonds takes energy. To start anychemical reaction, a minimum amount of energy is needed.This energy is called the activation energy of the reaction.

What term describes the minimum amount ofenergy needed to start a reaction?

What about reactions that release energy? Is there an activa-tion energy for these reactions too? Yes, even though they releaseenergy later, these reactions also need enough energy to start.

One example of a reaction that needs energy to start is theburning of gasoline. You have probably seen movies in which acar plunges over a cliff, lands on the rocks below, and suddenlybursts into flames. But if some gasoline is spilled accidentallywhile filling a gas tank, it probably will evaporate harmlessly ina short time.

Why doesn’t this spilled gasoline explode as it does in themovies? The reason is that gasoline needs energy to start burning.That is why there are signs at filling stations warning you not tosmoke. Other signs advise you to turn off the ignition, not to usemobile phones, and not to reenter the car until fueling is complete.

This is similar to the lighting of the Olympic Cauldron,as shown in Figure 12. Cauldrons designed for each Olympics con-tain highly flammablematerials that cannotbe extinguished byhigh winds or rain.However, they do not ignite until theopening ceremonieswhen a runner lightsthe cauldron using a flame that was kin-dled in Olympia,Greece, the site ofthe original OlympicGames.

Figure 12 Most fuels needenergy to ignite. The OlympicTorch, held by Cathy Freeman inthe 2000 Olympics, provided theactivation energy required to lightthe fuel in the cauldron.

Topic: Olympic TorchVisit forWeb links to information aboutthe Olympic Torch.

Activity With each newOlympics, the host city devises anew Olympic Torch. Research theprocess that goes into developingthe torch and the fuel it uses.

bookl.msscience.com

Victoria Arocho/AP/Wide World Photos



Reaction Rate Many physical processes are measured in terms of a rate. A

rate tells you how much something changes over a given periodof time. For example, the rate or speed at which you run or rideyour bike is the distance you move divided by the time it tookyou to move that distance. You may jog at a rate of 8 km/h.

Chemical reactions have rates, too. The rate of reaction tellshow fast a reaction occurs after it has started. To find the rate ofa reaction, you can measure either how quickly one of the reac-tants is consumed or how quickly one of the products is created,as in Figure 13. Both measurements tell how the amount of asubstance changes per unit of time.

What can you measure to determine the rate ofa reaction?

Reaction rate is important in industry because the faster theproduct can be made, the less it usually costs. However, some-times fast rates of reaction are undesirable such as the rates ofreactions that cause fruit to ripen. The slower the reaction rate,the longer the food will stay edible. What conditions control thereaction rate, and how can the rate be changed?

Temperature Changes Rate You can slow the ripening ofsome fruits by putting them in a refrigerator, as in Figure 14.Ripening is caused by a series of chemical reactions. Loweringthe temperature of the fruit slows the rates of these reactions.

Figure 14 Tomatoes are often pickedgreen and then held in refrigerated storageuntil they can be delivered to grocerystores.

Figure 13 The diminishingamount of wax in this candle as itburns indicates the rate of thereaction.

(t)Aaron Haupt, (bl)Kevin Schafer/CORBIS, (br)Icon Images


Meat and fish decompose faster at highertemperatures, producing toxins that can

make you sick. Keeping these foods chilled slows the decompo-sition process. Bacteria grow faster at higher temperatures, too,so they reach dangerous levels sooner. Eggs may contain suchbacteria, but the heat required to cook eggs also kills bacteria, sohard-cooked eggs are safer to eat than soft-cooked or raw eggs.

Temperature Affects Rate Most chemical reactions speedup when temperature increases. This is because atoms and mol-ecules are always in motion, and they move faster at higher tem-peratures, as shown in Figure 15. Faster molecules collide witheach other more often and with greater energy than slower mol-ecules do, so collisions are more likely to provide enough energyto break the old bonds. This is the activation energy.

The high temperature inside an oven speeds up the chemicalreactions that turn a liquid cake batter into a more solid, spongycake. This works the other way, too. Lowering the temperatureslows down most reactions. If you set the oven temperature toolow, your cake will not bake properly.

Concentration Affects Rate The closer reactant atomsand molecules are to each other, the greater the chance of colli-sions between them and the faster the reaction rate. It’s like thesituation shown in Figure 16. When you try to walk through acrowded train station, you’re more likely to bump into otherpeople than if the station were not so crowded. The amount ofsubstance present in a certain volume is called the concentrationof that substance. If you increase the concentration, you increasethe number of particles of a substance per unit of volume.

Figure 15 Molecules collidemore frequently at higher temper-atures than at lower temperatures.This means they are more likely toreact.

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Figure 16People are morelikely to collide incrowds. Moleculesbehave similarly.

Collisions are less frequentin a dilute solution.

Collisions are more frequent in aconcentrated solution.

SuperStock

Surface Area Affects Rate The exposed surface area ofreactant particles also affects how fast the reaction can occur.You can quickly start a campfire with small twigs, but starting afire with only large logs would probably not work.

Only the atoms or molecules in the outer layer of the reac-tant material can touch the other reactants and react. Figure 17Ashows that when particles are large, most of the iron atoms arestuck inside and can’t react. In Figure 17B, more of the reactantatoms are exposed to the oxygen and can react.

Slowing Down Reactions Sometimes reactions occur too quickly. For example, food

and medications can undergo chemical reactions that causethem to spoil or lose their effectiveness too rapidly. Luckily,these reactions can be slowed down.

A substance that slows down a chemical reaction is called aninhibitor. An inhibitor makes the formation of a certainamount of product take longer. Some inhibitors completely stopreactions. Many cereals and cereal boxes contain the compoundbutylated hydroxytoluene, or BHT. The BHT slows the spoilingof the cereal and increases its shelf life.

Figure 17 Iron atoms trapped inside this steel beam can-not react with oxygen quickly. More iron atoms are exposed tooxygen molecules in this steel wool, so the reaction speeds up.

Rust

Oxygen

Iron

Identifying InhibitorsProcedure1. Look at the ingredients

listed on packages ofcereals and crackers inyour kitchen.

2. Note the preservativeslisted. These are chemicalinhibitors.

3. Compare the date on thebox with the approximatedate the box was pur-chased to estimate shelflife.

Analysis1. What is the average shelf

life of these products?2. Why is increased shelf life

of such products important?

Figure 18 BHT, an inhibitor, isfound in many cereals and cerealboxes.

50 ◆ L CHAPTER 2(tl)Chris Arend/Alaska Stock Images/PictureQuest, (tr)Aaron Haupt, (b)Bryan F. Peterson/CORBIS


Speeding Up Reactions Is it possible to speed up a chemical reaction? Yes, you can

add a catalyst (KAT uh lihst). A catalyst is a substance thatspeeds up a chemical reaction. Catalysts do not appear in chem-ical equations, because they are not changed permanently orused up. A reaction using a catalyst will not produce more prod-uct than a reaction without a catalyst, but it will produce thesame amount of product faster.

What does a catalyst do in a chemical reaction?

How does a catalyst work? Many catalysts speed up reactionrates by providing a surface for the reaction to take place.Sometimes the reacting molecules are held in a particular posi-tion that favors reaction. Other catalysts reduce the activationenergy needed to start the reaction.

Catalytic Converters Catalysts are used in the exhaust sys-tems of cars and trucks to aid fuel combustion. The exhaustpasses through the catalyst, often in the form of beads coatedwith metals such as platinum or rhodium. Catalysts speed thereactions that change incompletely burned substances that are harmful, suchas carbon monoxide, into less harmfulsubstances, such as carbon dioxide.Similarly, hydrocarbons are changed intocarbon dioxide and water. The result ofthese reactions is cleaner air. These reac-tions are shown in Figure 19.

Figure 19 Catalytic convertershelp to complete combustion offuel. Hot exhaust gases pass overthe surfaces of metal-coatedbeads. On the surface of the beads,carbon monoxide and hydrocar-bons are converted to CO2 and H2O.

Oxygen

Carbon dioxideCarbon

monoxideHydro-carbon

Water

Bead coated with hot platinum

Breathe Easy The CleanAir Act of 1970 requiredthe reduction of 90 percentof automobile tailpipeemissions. The reductionof emissions included theamount of hydrocarbonsand carbon monoxidereleased. Automakersneeded to develop tech-nology to meet this newstandard. After much hardwork, the result of thislegislation was the intro-duction of the catalyticconverter in 1975.

Courtesy General Motors

Self Check1. Describe how you can measure reaction rates.

2. Explain in the general reaction A � B � energy → C,how the following will affect the reaction rate.

a. increasing the temperature

b. decreasing the reactant concentration

3. Describe how catalysts work to speed up chemical reactions.

4. Think Critically Explain why a jar of spaghetti saucecan be stored for weeks on the shelf in the market butmust be placed in the refrigerator after it is opened.

SummaryChemical Reactions

• To form new bonds in the product, old bondsmust break in the reactants. This takes energy.

• Activation energy is the minimum quantity of energy needed to start a reaction.

Reaction Rate

• The rate of reaction tells you how fast a reaction occurs.

• Temperature, concentration, and surface area affect the rate of reaction.

Inhibitors and Catalysts

• Inhibitors slow down reactions. Catalystsspeed up reactions.

• Enzymes are catalysts that speed up or slowdown reactions for your cells.

5. Solve One-Step Equations A chemical reaction is pro-ceeding at a rate of 2 g of product every 45 s. How long will it take to obtain 50 g of product?


Enzymes Are Specialists Some of the mosteffective catalysts are at work in thousands of reac-tions that take place in your body. These catalysts,called enzymes, are large protein molecules thatspeed up reactions needed for your cells to workproperly. They help your body convert food to fuel,build bone and muscle tissue, convert extra energyto fat, and even produce other enzymes.

These are complex reactions. Without enzymes,they would occur at rates that are too slow to beuseful or they would not occur at all. Enzymesmake it possible for your body to function. Like

other catalysts, enzymes function by positioning the reactingmolecules so that their structures fit together properly. Enzymesare a kind of chemical specialist—enzymes exist to carry outeach type of reaction in your body.

Other Uses Enzymes work outside your body, too. One classof enzymes, called proteases (PROH tee ay ses), specializes inprotein reactions. They work within cells to break down large,complex molecules called proteins. The meat tenderizer shownin Figure 20 contains proteases that break down protein inmeat, making it more tender. Contact lens cleaning solutionsalso contain proteases that break down proteins from your eyesthat can collect on your lenses and cloud your view.

Figure 20 The enzymes in meattenderizer break down protein inmeat, making it more tender.

bookl.msscience.com/self_check_quizMatt Meadows


LAB L ◆ 53

Real-World QuestionMatter can undergo two kinds of changes—physical and chemical. A physical change affectsonly physical properties. When a chemical changetakes place, a new product is produced. How can ascientist tell if a chemical change took place?

Goals■ Determine if a physical or chemical change

took place.

Materials500-mL Erlenmeyer flask100-mL graduated cylinderone-hole stopper with 15-cm length of glass

tube inserted1,000-mL beaker 45-cm length of rubber (or plastic) tubingstopwatch or clock with second handweighing dish balancebaking soda vinegar

Safety Precautions

WARNING: Vinegar (acetic acid) may cause skinand eye irritation.

Procedure1. Add about 300 mL of water to the 500-mL

Erlenmeyer flask.

2. Weigh 5 g of baking soda. Carefully pour thebaking soda into the flask. Swirl the flaskuntil the solution is clear.

3. Insert the rubber stopper with the glass tub-ing into the flask.

4. Add about 600 mL of water to the 1,000-mLbeaker.

5. Attach one end of the rubber tubing to thetop of the glass tubing. Place the other endof the rubber tubing in the beaker. Be surethe rubber tubing remains under the water.

6. Remove the stopper from the flask. Carefullyadd 80 mL of vinegar to the flask. Replacethe stopper.

7. Count the number of bubbles coming into thebeaker for 20 s. Repeat this two more times.

8. Record your data in your Science Journal.

Conclude and Apply1. Describe what you observed in the flask

after the acid was added to the baking soda solution.

2. Classify Was this a physical or chemicalchange? How do you know?

3. Analyze Results Was this processendothermic or exothermic?

4. Calculate the average reaction rate basedon the number of bubbles per second.

Physical or Chemical Change?

Compare your results with those of otherstudents in your class.

Matt Meadows

Design Your OwnDesign Your Own


Real-World QuestionEnergy is always a part of a chemical reaction. Some reac-tions need a constant supply of energy to proceed. Otherreactions release energy into the environment. What evi-dence can you find to show that a reaction between hydro-gen peroxide and liver or potato is exothermic orendothermic?

Form a HypothesisMake a hypothesis that describes how you can use the reactions between hydrogen peroxide and liver or potato to determine whether a reaction is exothermic or endothermic.

Test Your HypothesisMake a Plan1. As a group, look at the list of materials. Decide which procedure

you will use to test your hypothesis, and which measurements youwill make.

2. Decide how you will detect the heat released to the environmentduring the reaction. Determine how many measurements you willneed to make during a reaction.

3. You will get more accurate data if you repeat each experiment sev-eral times. Each repeated experiment is called a trial. Use the aver-age of all the trials as your data for supporting your hypothesis.

4. Decide what the variables are and what your control will be.

5. Copy the data table in your Science Journal before you begin tocarry out your experiment.

Follow Your Plan1. Make sure your teacher approves your plan before you start.

2. Carry out your plan.

3. Record your measurements immediately in your data table.

4. Calculate the averages of your trial results and record them inyour Science Journal.

Goals■ Design an experiment

to test whether a reac-tion is exothermic orendothermic.

■ Measure the tempera-ture change caused bya chemical reaction.

Possible Materialstest tubes (8)test-tube rack3% hydrogen peroxide

solutionraw liverraw potatothermometerstopwatchclock with second hand25-mL graduated cylinder

Safety Precautions

WARNING: Hydrogen per-oxide can irritate skin andeyes and damage clothing.Be careful when handlingglass thermometers. Testtubes containing hydro-gen peroxide should beplaced and kept in racks.Dispose of materials asdirected by your teacher.Wash your hands whenyou complete this lab.

Exothermic or Endothermic?

Amanita Pictures

Analyze Your Data

1. Can you infer that a chemical reaction took place? What evi-dence did you observe to support this?

2. Identify what the variables were in this experiment.

3. Identify the control.

Conclude and Apply1. Do your observations allow you to distinguish between an

exothermic reaction and an endothermic reaction? Useyour data to explain your answer.

2. Where do you think that the energy involved in thisexperiment came from? Explain your answer.

Compare the results obtained by yourgroup with those obtained by other groups.Are there differences? Explain how thesemight have occurred.

Temperature After Adding Liver/Potato

Trial Temperature After Temperature After Adding Liver (°C) Adding Potato (°C)

Starting After____min Starting After____min

1

2

3

4

LAB L ◆ 55Bob Daemmrich

Do not write in this book.

Diamonds are the most dazzling, most dra-matic, most valuable natural objects onEarth. Strangely, these beautiful objects

are made of carbon, the same material graphite—the stuff found in pencils—is made of. So why is adiamond hard and clear and graphite soft andblack? A diamond’s hardness is a result of howstrongly its atoms are linked. What makes a dia-mond transparent is the way its crystals arearranged. The carbon in a diamond is almostcompletely pure, with trace amounts of boron andnitrogen in it. These elements account for themany shades of color found in diamonds.

A diamond is the hardest naturally occurringsubstance on Earth. It’s so hard, only a diamondcan scratch another diamond. Diamonds areimpervious to heat and household chemicals.Their crystal structure allows them to be split (orcrushed) along particular lines.

Diamonds are made when carbon issqueezed at high pressures and temperatures inEarth’s upper mantle, about 150 km beneath thesurface. At that depth, the temperature is about1,400°C, and the pressure is about 55,000 atmos-pheres greater than the pressure at sea level.

As early as the 1850s, scientists tried to con-vert graphite into diamonds. It wasn’t until 1954that researchers produced the first synthetic dia-monds by compressing carbon under extremelyhigh pressure and heat. Scientists convertedgraphite powder into tiny diamond crystalsusing pressure of more than 68,000 atm, and a temperature of about 1,700°C for about 16 hours.

Synthetic diamonds are human-made, butthey’re not fake. They have all the properties ofnatural diamonds, from hardness to excellentheat conductivity. Experts claim to be able todetect synthetics because they contain tinyamounts of metal (used in their manufacturingprocess) and have a different luminescence thannatural diamonds. In fact, most synthetics aremade for industrial use. One major reason is thatmaking small synthetic diamonds is cheaperthan finding small natural ones. The other rea-son is that synthetics can be made to a requiredsize and shape. Still, if new techniques bringdown the cost of producing large, gem-qualitysynthetic diamonds, they may one day competewith natural diamonds as jewelry.

Research Investigate the history of diamonds—natural andsynthetic. Explain the differences between them and their uses.Share your findings with the class. For more information, visit

SCIENCEAND

HISTORYSCIENCE

CAN CHANGE THE COURSE OF HISTORY!

Almost theReal Thing

NaturalDiamond

SyntheticDiamond

bookl.msscience.com/time

(l)Tino Hammid Photography, (r)Joe Richard/UF News & Public Affairs


Formulas and Chemical Equations

1. Chemical reactions often cause observablechanges, such as a change in color or odor,a release or absorption of heat or light, or arelease of gas.

2. A chemical equation is a shorthand methodof writing what happens in a chemical reac-tion. Chemical equations use symbols torepresent the reactants and products of areaction, and sometimes show whetherenergy is produced or absorbed.

3. The law of conservation of mass requires abalanced chemical reaction that containsthe same number of atoms of each elementin the products as in the reactants. This istrue in every balanced chemical equation.

Rates of ChemicalReactions

1. The rate of reaction is a measure of howquickly a reaction occurs.

2. All reactions have an activation energy—a certain minimum amount of energyrequired to start the reaction.

3. The rate of a chemical reaction can be influenced by the temperature, the concen-tration of the reactants, and the exposed sur-face area of the reactant particles.

4. Catalysts can speed up a reaction withoutbeing used up. Inhibitors slow down therate of reaction.

5. Enzymes are protein molecules that act ascatalysts in your body’s cells.

CHAPTER STUDY GUIDE L ◆ 57

Copy and complete the following concept map on chemical reactions.

Chemical Reactions

Concentration

influenced bysped up by

slowed down by

rates of reaction

Absorbed

thermal energy is thermal energy is

Exothermic

types of

bookl.msscience.com/interactive_tutorbookl.msscience.com/interactive_tutorDavid Young-Wolff/PhotoEdit, Inc.


Explain the differences between the vocabularyterms in each of the following sets.

1. exothermic reaction—endothermic reaction

2. activation energy—rate of reaction

3. reactant—product

4. catalyst—inhibitor

5. concentration—rate of reaction

6. chemical equation—reactant

7. inhibitor—product

8. catalyst—chemical equation

9. rate of reaction—enzyme

Choose the word or phrase that best answers thequestion.

10. Which statement about the law of conser-vation of mass is NOT true?A) The mass of reactants must equal the

mass of products.B) All the atoms on the reactant side of an

equation are also on the product side.C) The reaction creates new types of

atoms.D) Atoms are not lost, but are rearranged.

11. To slow down a chemical reaction, whatshould you add?A) catalyst C) inhibitorB) reactant D) enzyme

12. Which of these is a chemical change?A) Paper is shredded.B) Liquid wax turns solid.C) A raw egg is broken.D) Soap scum forms.

13. Which of these reactions releases thermalenergy?A) unbalanced C) exothermicB) balanced D) endothermic

14. A balanced chemical equation must havethe same number of which of these onboth sides of the equation?A) atoms C) moleculesB) reactants D) compounds

15. What does NOT affect reaction rate?A) balancing C) surface areaB) temperature D) concentration

16. Which is NOT a balanced equation?A) CuCl2 � H2S → CuS � 2HCl

B) AgNO3 � NaI → AgI � NaNO3

C) 2C2H6 � 7O2 → 4CO2 � 6H2O

D) MgO � Fe → Fe2O3 � Mg

17. Which is NOT evidence that a chemical reaction has occurred?A) Milk tastes sour.B) Steam condenses on a cold window.C) A strong odor comes from a broken egg.D) A slice of raw potato darkens.

18. Which of the following would decrease therate of a chemical reaction?A) increase the temperatureB) reduce the concentration of a reactantC) increase the concentration of a reactantD) add a catalyst

19. Which of these describes a catalyst?A) It is a reactant.B) It speeds up a reaction.C) It appears in the chemical equation.D) It can be used in place of an inhibitor.

58 ◆ L CHAPTER REVIEW

activation energy p. 47catalyst p. 51chemical equation p. 192chemical reaction p. 190concentration p. 49endothermic reaction

p. 43

enzyme p. 52exothermic reaction p. 43inhibitor p. 50product p. 38rate of reaction p. 48reactant p. 38

bookl.msscience.com/vocabulary_puzzlemaker


20. Cause and Effect Pickled cucumbers remainedible much longer than fresh cucumbersdo. Explain.

21. Analyze A beaker of water in sunlightbecomes warm. Has a chemical reactionoccurred? Explain.

22. Distinguish if 2Ag � S is the same as Ag2S.Explain.

23. Infer Apple slices can be kept from brown-ing by brushing them with lemon juice.Infer what role lemon juice plays in thiscase.

24. Draw a Conclusion Chili can be made usingground meat or chunks of meat. Whichwould you choose, if you were in a hurry?Explain.

Use the graph below to answer question 25.

25. Interpret Scientific Illustrations The two curveson the graph represent the concentrationsof compounds A (blue) and B (red) dur-ing a chemical reaction.a. Which compound is a reactant? b. Which compound is a product? c. During which time period is the

concentration of the reactant changingmost rapidly?

26. Form a Hypothesis You are cleaning out acabinet beneath the kitchen sink and findan unused steel wool scrub pad that hasrusted completely. Will the remains of thispad weigh more or less than when it wasnew? Explain.

27. Poster Make a list of the preservatives inthe food you eat in one day. Present yourfindings to your class in a poster.

Rate of Reaction

Time (min)

Con

cen

trat

ion

(g/L

)

1 2 3 4 5

A

B

CHAPTER REVIEW L ◆ 59

Use the graph below to answer question 28.

28. Reaction Rates In the reaction graph above, howlong does it take the reaction to reach 50�C?

29. Chemical Equation In the following chemicalequation, 3Na � AlCl3 → 3NaCl � Al, howmany aluminum molecules will be produced if you have 30 molecules of sodium?

30. Catalysis A zinc catalyst is used to reduce the reaction time by 30%. If the normal time for the reaction to finish is 3 h, how long will ittake with the catalyst?

31. Molecules Silver has 6.023 � 1023 moleculesper 107.9 g. How many molecules are there ifyou have

a. 53.95 g?

b. 323.7 g?

c. 10.79 g?

Reaction RateTe

mp

(°C

)

406080

200

10 2 43 5 6Time (min)

bookl.msscience.com/chapter_review


Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

Use the photo below to answer questions 1 and 2.

1. The photograph shows thereaction of copper (Cu) with silver nitrate (AgNO3)to produce copper nitrate(Cu(NO3)2) and silver (Ag). Thechemical equation that describesthis reaction is the following:

2AgNO3 � Cu →Cu(NO3)2 � 2Ag

What term describes what ishappening in the reaction?A. catalystB. chemical changeC. inhibitorD. physical change

2. Which of the following terms describes thecopper on the left side of the equation?A. reactant C. enzymeB. catalyst D. product

3. Which term best describes a chemical reaction that absorbs thermal energy?A. catalytic C. endothermicB. exothermic D. acidic

4. What should be balanced in a chemicalequation?A. compounds C. moleculesB. atoms D. molecules and atoms

Use the photo below to answer questions 5 and 6.

5. The photograph above shows a demonstra-tion of electrolysis, in which water is bro-ken down into hydrogen and oxygen.Which of the following is the best way towrite the chemical equation for thisprocess?A. H2O � energy → H2 � O2

B. H2O � energy → 2H2 � O2

C. 2H2O � energy → 2H2 � O2

D. 2H2O � energy → 2H2 � 2O2

6. For each atom of hydrogen that is presentbefore the reaction begins, how manyatoms of hydrogen are present after thereaction?A. 1 C. 4B. 2 D. 8

7. What is the purpose of an inhibitor in achemical reaction?A. decrease the shelf life of foodB. increase the surface areaC. decrease the speed of a chemical

reactionD. increase the speed of a chemical

reaction

Electrical energyfrom a battery

Hydrogen (H2)

Oxygen (O2)

Water (H2O)

60 ◆ L STANDARDIZED TEST PRACTICE

Read All Questions Never skip a question. If you are unsure ofan answer, mark your best guess on another sheet of paperand mark the question in your test booklet to remind you tocome back to it at the end of the test.

Lester V. Bergman/CORBIS

STANDARDIZED TEST PRACTICE L ◆ 61

Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

8. If the volume of a substance changes butno other properties change, is this a physi-cal or a chemical change? Explain.

Use the equation below to answer question 9.

CaCl2 � 2AgNO3 → 2 � Ca(NO3)2

9. When solutions of calcium chloride(CaCl2) and silver nitrate (AgNO3) aremixed, calcium nitrate (Ca(NO3)2) and awhite precipitate, or residue, form.Determine the chemical formula of the precipitate.

Use the illustration below to answer questions 10 and 11.

10. The figure above demonstrates the move-ment of atoms at temperatures of 0°C and100°C. What would happen to the move-ment of the atoms if the temperaturedropped far below 0°C?

11. Describe how the difference in the movement of the atoms at two differenttemperatures affects the rate of mostchemical reactions.

12. Is activation energy needed for reactionsthat release energy? Explain.

Record your answers on a sheet of paper.

Use the illustration below to answer questions 13 and 14.

13. The photograph above shows a forest firethat began when lightning struck a tree.Describe the chemical reaction that occurswhen trees burn. Is the reaction endother-mic or exothermic? What does this mean?Why does this cause a forest fire to spread?

14. The burning of logs in a forest fire is achemical reaction. What prevents thischemical reaction from occurring whenthere is no lightning to start a fire?

15. Explain how the surface area of a materialcan affect the rate at which the materialreacts with other substances. Give anexample to support your answer.

16. One of the chemical reactions that occursin the formation of glass is the combiningof calcium carbonate (CaCO3) and silica(SiO2) to form calcium silicate (CaSiO3)and carbon dioxide (CO2):

CaCO3 � SiO2 → CaSiO3 � CO2

Describe this reaction using the names ofthe chemicals. Discuss which bonds arebroken and how atoms are rearranged toform new bonds.

Container A Container B

bookl.msscience.com/standardized_testPeter Walton/Index Stock


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