Endothermic reactions absorb energy. - ClassZone

1 The bombardier beetle, shown in the photograph onthe right, uses natural exothermic reactions to defenditself. Although several chemical reactions are involved,the end result is the production of a hot, toxic most important reaction in the process is the decom-position of hydrogen peroxide into water and 2H2O + O2 First, the hydrogen peroxide rapidly breaks a hot, toxic mixture is made by the reactions . Oxygen gas fromthe reaction in the equation above puts the mixture under enough pressure builds up, the beetle can spray the reactions absorb reactions often produce a decrease in Endothermic reactions , the bond energies of the reactants are greaterthan the bond energies of the products. As a result, more energy isneeded to break the bonds in the reactants than is released during theformation of the products.

2 The difference in energy is usually absorbedfrom the surroundings as heat. This often causes a decrease in thetemperature of the reaction Endothermic reactions absorb energy . However, they do not allabsorb energy as heat. One example of this type of Endothermic reac-tion is the decomposition of water by electrolysis. In this case, the energythat is absorbed is in the form of electrical energy . When the electriccurrent is turned off, the reaction stops. The change in energy thatoccurs in this reaction is shown tipThe prefix endo- means inside. What information in the diagram shows that the decomposition of water is Endothermic ?reactants2H2 OenergyaddedMore energy is addedthan ReactionsChapter 9:Chemical Reactions291 Electrolysis of WaterThe products have lower bond energiesthan the broken inreactantsbonds formed in products2H2+ O2energyreleasedOHHOHHOOHHHOHHOHHHs8pe-3 0903-ca 12/6/05 4:33 PM Page 291 MAZER PDF