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■ Determine how chemical energyis transformed.■ Explain how reaction rates arechanged.Chemical energy makes it possiblefor your body to move, grow, andstay warm.Chemical EnergyChemical Reactions and EnergyOn a hot summer night, you might have seen fireflies glowing,like those in Figure 21. Did you ever wonder how they maketheir eerie, blinking light? If you have seen light sticks, whichglow for a short period of time, you have observed the sameprocess that causes the fireflies’ glow. Energy in the form of lightis released when a chemical reaction takes place inside the lightstick. A burner on a gas stove releases heat and light energybecause of a chemical reaction taking place. You might not realizeit, but every day you make use of the energy released by manychemical reactions.(l)Runk/Schoenberger from Grant Heilman Photography, (r)Laura Riley/Bruce Coleman, Inc./PictureQuestReview Vocabularychemical bonds: the forces holdingatoms together in a moleculeNew Vocabularyendothermic reactionexothermic reaction• catalystFigure 21 Chemical reactionscan release light energy.What is a chemical reaction? In a chemical reaction,compounds are broken down or new compounds are formed.Sometimes both processes occur. Some chemical reactionsoccur when atoms or molecules come together. New compoundsare formed when atoms and molecules combine andbonds form between them. A compound is broken down whenthe bonds between the atoms that make up the compound arebroken. These atoms are then available to recombine to formnew compounds.When a fire burns, a chemical reaction occurs. Bondsbetween the atoms in some of the compounds that make up thewood are broken. These atoms then combine with atoms in theair and form new compounds. As these new compounds areformed, heat and light are given off.Each point of greenish light in this picture is a firefly.A chemical reactioninside a firefly’s bodyreleases light.178 CHAPTER 6 Energy