Q. Consider the reaction $2A + B \rightarrow product$ When concentration of B alone was doubled, the half-life did not change. When the concentration of A alone was doubled, the rate increased by two times. The unit of rate constant for this reaction is
A) $L\ mol^{- 1}s^{- 1}$
B) No unit
C) $mo{l\ L}^{- 1}s^{- 1}$
D) $s^{- 1}$
Explanation
(a)
$2A + B \rightarrow product$
[B] is doubled, half-life didn’t change
Half-life is independent of change in concentration of reactant i.e., first order
First order w.r.t. to B
When [A] is doubled, rate increased by two times
$\Rightarrow$ First order w.r.t.A
Hence, net order of reaction =1+1=2
Unit for the rate constant=$conc.^{(1 - n)}t^{- 1}$
$= \left( mol^{- 1} \right)^{- 1}.s^{- 1}$
$L.\ mol^{- 1}s^{- 1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.