At  t = 0, the concentration of the reactant R = [R]0, where [R]0 is
initial concentration of the reactant Substituting in equation (3 5)
[R]0
= –k × 0 + I
[R]0
= I
Substituting the value of I in the equation (3 5)
[R]
= -kt + [R]0
(3