Chemical Kinetics Question 75
Question: For a reactions $ A+B\to $ product, it was found that rate of reaction increases four times if concentration of -A- is doubled, but the rate of reaction remains unaffected. If concentration of -B- is doubled. Hence, the rate law for the reaction is [MP PET/PMT 1998; MP PMT 2003]
Options:
A) $ rate=k[A][B] $
B) $ rate=k{{[A]}^{2}} $
C) $ rate=k{{[A]}^{2}}{{[B]}^{1}} $
D) $ rate=k{{[A]}^{2}}{{[B]}^{2}} $
Show Answer
Answer:
Correct Answer: B
Solution:
Let the rate of reaction depends on xth power of [A]. Then
$ r_1=k{{[A]}^{x}} $ and $ r_2=k{{[2A]}^{x}} $
$ \therefore \frac{r_1}{r_2}=\frac{{{[A]}^{x}}}{{{[2A]}^{x}}}=\frac{1}{4}={{( \frac{1}{2} )}^{2}} $
$ (\because r_2=4r_1) $
$ \therefore x=2 $ . As the reaction rate does not depend upon the concentration of B. Hence, the correct rate law will be $ rate=K{{[A]}^{2}}{{[B]}^{o}} $ or $ =K{{[A]}^{2}} $
