For example a reactant. Rate of reaction examples. Chemical Equilibrium Reaction Online College Chemistry Courses College Chemistry Online Degree Chemical Kinetics The reaction rate also known as the rate of reaction is the rate at which a chemical reaction occurs and is proportional to the increase in product concentration per unit time and the decrease in reactant concentration per unit time. . The rate of reaction can be analysed. The instantaneous rate of reaction is the speed at which the reaction takes place at a given time. 4 Its unit is m o l L 1 c m 1. In chemistry the rate of a reaction is defined by either the rate of disappearance of a reactant or the rate of appearance of a product. Since at temperature T the molecules have energies given by a Boltzmann distribution one can expect the number of collisions with energy greater than Ea to be proportional to e. Mean rate of reaction 60g15s 4gs. Re