Similarly, the speed of  a reaction or  the rate of a
reaction can be defined as the change in concentration of  a reactant
or product in unit time To be more specific, it can be expressed in
terms of:
(i) the rate of decrease in concentration of any one of the
reactants, or
(ii) the rate of increase in concentration of any one of the products Consider a hypothetical reaction, assuming that the volume of the
system remains constant R ® P
One mole of the reactant R produces one mole of the product P