# Dependence of reaction rate on concentrations and stoichiometric coefficients of reactants and products

Consider a general equation of a reaction:

$$\ce{aA + bB -> \text{Products}}$$

We can say, in chemical kinetics, that the rate of the reaction is:

$$\text{Rate} = k([\ce{A}]^a [\ce{B}]^b)$$

where $\ce{[A]}$, $\ce{[B]}$ are the concentrations or active masses of the reactants.

My question is, why is the rate of reaction proportional to the concentrations of the reactants raised to the power of their stoichiometric coefficients ?

(Not really the point of the question, but why to the power and not just a product of the coefficients?)