Question

For a reaction $2A + B \to$ Products, doubling the initial concentration of both the reactants increases the rate by a factor of $8$, and doubling the concentration of $B$ alone doubles the rate. The rate law for the reaction is

• A. $r=k\left[A\right]\left[B\right]^{2}$
• B. $r=k\left[A\right]^{2}\left[B\right]$
• C. $r=k\left[A\right]\left[B\right]$
• D. $r=k\left[A\right]^{2}\left[B\right]^{2}$

Answer 1

Answer: (B)

$2A + B \to$ Products,
According to question: Rate of reaction of$A\propto\left[B\right]$ as increase in rate is double when $\left[B\right]$ is doubled.
Rate of reaction $\propto\left[A\right]^{2}\left[B\right]$ as increase in rate is 8 times when concentration of both reactant is doubled. It means that order of reaction is $3$ and overall rate reaction should be
$r=k\left[A\right]^{2}\left[B\right]$