Chapter 16 Chemical Equilibrium CHM 130 GCC Chemistry

Chapter 16: Chemical Equilibrium CHM 130 GCC Chemistry

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 activation energy, Ea. the molecules must be oriented correctly. http: //www. mhhe. com/physsci/chemistry/animations/chang_2 e/orient ation_of_collision. swf

Collision Theory – Effective Collisions Cl + NOCl → Cl 2 + NO Correct orientation to facilitate reaction Incorrect orientation does not favor reaction An effective collision results in reaction. An ineffective collision results in no reaction.

Rates of Reaction 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 = product heat – reactant heat Endothermic = reactants gain or absorb heat, heat is a reactant, heat enters the rxn; DH is positive (> 0) Reactants + Heat Products Exothermic = reactants lose or release heat, heat is a product, heat exits the rxn; DH is negative (< 0) Reactants Products + Heat

Energy Profiles Exothermic, is DH + or -? -

16. 2 Energy Profiles Endothermic, is DH + or -? +

16. 2 Energy Profiles With Catalyst

Chapter 16 Self-Test, p. 492 Try 1 -2 Answers in Appendix J

Chapter 16 Quiz Draw the energy profile for an endothermic reaction. Label the: Transition State (T. S. ) DH Reactants Products EA