The rate constant of a reaction is k = 3.0x10^-4 mol L^-1 s^-1 at a given temperature. Select the correct statements.

The rate stays at 3.0x10^-4 mol L^-1 s^-1 even when the concentration of the reactant is halved.

A concentration decrease of 0.045 mol L^-1 takes 150 s (as long as the reactant is not exhausted).

The rate stays at 3.0x10^-4 mol L^-1 s^-1 even when the concentration of the reactant is halved.

A concentration decrease of 0.045 mol L^-1 takes 150 s (as long as the reactant is not exhausted).

The reaction must be unimolecular.

JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ck033

The rate constant of a reaction is $k = 3.0 \times 1 0^{- 4} mol L^{- 1} s^{- 1}$ at a given temperature. Select the correct statements.

AThe reaction is of zero order.
BThe rate stays at $3.0 \times 1 0^{- 4} mol L^{- 1} s^{- 1}$ even when the concentration of the reactant is halved.
CA concentration decrease of $0.045 mol L^{- 1}$ takes $150 s$ (as long as the reactant is not exhausted).
DThe reaction must be unimolecular.

A rate constant with the unit of rate means rate

= k [A]^{0}

, zero order, so the rate does not depend on concentration. The time for a fall of

0.045 M

0.045/3.0 \times 1 0^{- 4} = 150 s

. Order does not fix molecularity (zero-order reactions are typically multi-step or surface reactions), so the last statement is not justified.