The chemical reactions differ primarily in the speed at which they take place. Some take years to attain equilibrium, while some are basically instantaneous. The rate of reaction of a given chemical reaction is the determination of the change in the concentration of the products or the change in the concentration of the reactants per unit time.
With time, as the reaction reaches dynamic equilibrium, the concentration of the reactants, that is, A and B reduce and the concentration of the product, that is, C elevates. This is due to the fact that the chemical reactions seem to shift towards the product(s) end.