Chapter 16 CHM 130 GCC

16.1 Collision Theory Molecules must hit/collide in order to react and make products A successful collision results in reactant bonds breaking and/or product bonds forming To increase the # of successful collisions: you need more collisions. you need enough energy, Ea, activation energy. the molecules must be oriented correctly. http://www.mhhe.com/physsci/chemistry/animations/chang_2e/orientation_of_collision.swf

To Increase the Rate of Reaction Increase [reactant], more reactants = more collisions Increase temperature, molecules move faster = more collisions AND more energy Add a catalyst which provides an alternate reaction pathway with lower Ea Activation Energy, Ea, is the minimum energy needed to react (turn reactants to products)

16.2 Energy Profiles Transition state = in between reactants and products, the reactant bonds are ½ broken and product bonds ½ formed, so this is a very high energy and unstable species, exists less than a millisecond DH = change in heat energy = product’s heat – reactant’s heat Endothermic = reactants gain or absorb heat, heat is a reactant, heat enters the rxn Reactants + Heat g Products Exothermic = reactants lose or release heat, heat is a product, heat exits the rxn Reactants g Products + Heat

Exothermic, is DH + or -? -

Draw the energy profile for an endothermic reaction Label the TS DH Reactants Products EA

Endothermic, is DH + or -? +

With Catalyst

Self Test Page 477 Try 1-2, 10 Answers in Appendix J