Question

The rate equation for the reaction $2A+B\to C$ is found to be : $rate=k\left[A\right]\left[B\right].$ The correct statement in relation to this reaction is:

• A. unit of $k$ must be $s^{-1}$
• B. $t_{1/2}$ is a constant
• C. rate of formation of $C$ is twice the rate of disappearance of $A$
• D. value of $k$ is independent of the initial concentrations of $A$ and $B$

Answer 1

The correct option is D value of $k$ is independent of the initial concentrations of $A$ and $B$

2A+B $⟶$ C.

Rate = $K\left[A\right]\left[B\right]$

$\bullet$ order of the given reaction = 2.

$\therefore t_{1/2}$ is not constant. It is constant only for a first order reaction.

$\therefore$ Unit of K for $n^{th}$ order reaction is $M^{(1-n)}{time}^{-1}$ for a $2^{nd}$ order reaction it is $M^{-1}{S}^{-1}$

$\therefore$ As per rate law :

$\frac{-1}{2}\frac{d\left[A\right]}{dt}=\frac{d\left[C\right]}{dt}$

$\therefore$ The rate of formation of C is half of the rate of disappearance of A.

$\therefore$ The rate constant is independent of the initial concentrations of the reactants. As k only changes when temperature chnages.