The reactions $\left(\mathrm{I}\right)2\mathrm{NO}+{\mathrm{O}}_2\to 2{\mathrm{NO}}_2 \left(\mathrm{II}\right) 2\mathrm{CO}+{\mathrm{O}}_2\to 2{\mathrm{CO}}_2$   look to be identical, yet the first is faster than the second. The reason is that

Minimum energy required for the reactant 'A' to convet to product 'B' is called thresold energy.

Reactant 'A' has to gain an energy called activation enrgy, Ea to attain threshold energy.

Thus lesser the activation energy greater will be the rate of chemical reaction.

Activation energy of the reaction,

is less because it involves lesser bond rearrangements.

Activation energy of the reaction, 

is high because it involves more bond rearrangements.