Chemical Kinetics - Result Question 29

####29. Consider a reaction, $a G+b H \rightarrow$ products. When concentration of both the reactants $G$ and $H$ is doubled, the rate increases by eight times. However, when concentration of $G$ is doubled keeping the concentration of $H$ fixed, the rate is doubled. The overall order of the reaction is

(2007, 3M)

(a) 0

(b) 1

(c) 2

(d) 3

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Answer:

Correct Answer: 29. (a)

Solution:

  1. Rate $\propto[G]^{m}[H]^{n}$

$\because$ Rate is double on doubling the concentration of $G$ and maintaining $H$ constant, $m=1$, i.e. $R \propto[G]$.

Also, when both concentration of $G$ and $H$ are doubled, rate increases by a factor of 8 . Here rate is increasing by a factor of 2 due to $G$ (first order in $G$ ), therefore, factor due to $H$ is 4 .

$$ \begin{array}{lll} \Rightarrow & R & \propto[H]^{2} \ \Rightarrow & \text { Overall order } & =m+n=1+2=3 \end{array} $$



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