Chapter 3: Rate Laws

Additional Homework Problems

CDP3-A

For families of reactions, the Polanyi-Semenov equation can be used to estimate activation energies from the heats of reaction, according to the equation,

E = C - ()

where and C are constants. For expthermic reactions, = -0.25 and C = 48 kJ/mol, while for endothermic reactions, = -0.75 and C = 48kJ/mol. However, these values may vary somewhat from reaction family to reaction family [K.J. Laidler, Theories of Chemical Reaction Rates (New York, R. E. Krieger, 1979), p. 38]. (Also see Appendix J)

(a)Why is this a reasonable correlation?

Consider the following family of reactions:

(b)Estimate the activation energy for the reaction

which has an exothermic heat of reaction of 6 kcal/mol (i.e., = -6 kcal/mol)