Chapter 15, Problem 102E

Consider the two reactions:

$\text{O}+{\text{N}}_{\text{2}}\to \text{NO}+\text{N}$E_a= 315 kJ/mol
$\text{Cl}+{\text{H}}_{\text{2}}\to \text{HCl}+\text{H}$E_a= 23 KJ/ mol

a. Why is the activation barrier for the first reaction so much higher than that for the second?
b. The frequency factors for these two reactions are very close to each other in value. Assuming that they are the same, calculate the ratio of the reaction rate constants for these two reactions at 25°C.