1 can you suggest why the activation barrier for the first

Question

Consider the two following reactions: 

O+N₂ ---> NO + N        E_a = 315 kJ/mol

Cl+H₂ ---> HCl + H        E_a = 23 kJ/mol

1. Can you suggest why the activation barrier for the first reaction is so much higher than that for the second?

2. The frequency factors for these two reactions are very close to each other in value. Assuming that they are the same, compute the ratio of the reaction rate constants for these two reactions at 25 degrees celcius.