Consider a reaction,

R → P t=0

Here R is the reactant and P is the product.

Rate = k[R]⁰ t=t

(Instantaneous rate) –dR/dt = k

dR =-kdt

On integrating both sides,

[R] = -kt + I

At t = 0,

[R]= [R₀] which makes I= R₀

[R] = [R₀]– kt. ………………………..i)

Here [R] = concentration of reactant at time ‘t’.

[R₀] = initial concentration of the reactant.

This reaction is known as the integrated rate equation of zero order.

After completion of zero order reaction [R]= 0

Using [R]= 0 in i)

[R₀]=kt

t=[R₀]/k