Choose the correct statements for a zero order reaction

(A) The rate of the reaction is independent of the initial concentration of the reactant
(B) The rate of the reaction increases linearly as the initial concentration of the reactant is increased
(C) The plot of concentration against time is a straight line with a positive slope
(D) The unit of rate constant is $mol\, L^{-1} s^{-1}$

Choose the correct answer from the options given below.

(A) and (D) only

The correct answer is Option (1) → (A) and (D) only

For a zero order reaction, the rate of reaction is independent of the concentration of the reactant.

The rate law is: Rate = k

This means the rate remains constant during the reaction and does not depend on the concentration of reactants.

The integrated rate equation for a zero order reaction is: [A] = [A]₀ − kt

From this equation:

• Concentration decreases linearly with time

• The plot of concentration vs time is a straight line with a negative slope

The unit of rate is: mol L⁻¹ s⁻¹

Since Rate = k for zero order reactions, the unit of rate constant k is also mol L⁻¹ s⁻¹.

• (A) The rate is independent of initial concentration: This is correct. For a zero-order reaction, the rate law is $Rate = k[A]^0$, which simplifies to $Rate = k$. This means the rate remains constant regardless of how much reactant is initially present or remains in the system.
• (B) Rate increases linearly with concentration: This is incorrect. In zero-order reactions, the rate is constant ($k$). A linear increase of rate with concentration is a characteristic of first-order reactions ($Rate = k[A]^1$).
• (C) Plot of concentration vs. time has a positive slope: This is incorrect.  For a zero order reaction, the plot of concentration vs time is a straight line but with a negative slope, because concentration decreases with time.

• (D) The unit of rate constant is $\text{mol L}^{-1} \text{s}^{-1}$: This is correct  because for zero order reactions: Rate = k So the unit of k is the same as the unit of rate.