But experimentally , it is observed that the rate of reaction is found to depend upon ‘ α ’ concentration terms of A and ‘ β ’ concentration terms of B Then ,
Rate α [ A ] α [ B ] β = k [ A ] α [ B ] β
where , [ A ] and [ B ] molar concentrations of A and B respectively and k is the velocity constant or rate constant . The above expression is known as rate law .
Rate Constant
In the above expression , k is called rate constant or velocity constant .
Rate constant may be defined as the specific rate of reaction when the molar concentrations of the reactants is taken to be unity , i . e .,
Rate = k , if [ A ] = [ B ] = 1
Units of rate constant or specific reaction rate for a nth order reaction is given as
K = ( 1 / Time ) x ( 1 /[ Conc .] n – 1 )