A reaction mechanism has three elementary steps

CHEMISTRY · Subjective · A Level · Chemistry · Kinetics · Kinetics

Problem

A reaction mechanism has three elementary steps. The first transition state is

45\,\text{kJ}\,\text{mol}^{-1}

above the reactants, the second is

20\,\text{kJ}\,\text{mol}^{-1}

above the intermediate formed after step 1, and the third is

15\,\text{kJ}\,\text{mol}^{-1}

above the intermediate formed after step 2. Explain why the first elementary step controls the overall rate of the reaction.