(a) What is the difference between an average rate and an instantaneous rate? (b) What is the difference between an initial rate and an instantaneous rate?

The rate of a reaction is the speed at which the reactants undergo transformation to the products at a constant temperature. The rate of a reaction is depended on many factors like temperature, pressure, surface area, catalysts, etc.

The average rate can be defined as the rate of a reaction in a particular interval of time and instantaneous rate can be defined as the rate of a reaction at a particular instant of time. These two concepts are different with the difference in the time considered.

The initial rate is the rate at the initial stage of the reaction and instantaneous rate can be defined as the rate of a reaction at a particular instant of time. Both are different in the sense that instantaneous rate can be taken at the initial stage of the reaction also.