Chemical Kinetics Question 287
Question: Consider the two hypothetical reactions given below:
I $ aA\to $ Products, $ k=x,mo{l^{-1}}Lmi{n^{-1}} $
II $ bB\to $ Products, $ k=y,mi{n^{-1}} $
The half-lives of both the reactions are the same, equal to 1 hr when molar concentration of the reactant is 1.0 M in each case. If these reactions are started at the same time taking 1M of the reactant in each case, the ratio [A]/[B] after 3 hr will be:
Options:
A) 0.5
B) 4
C) 1
D) 2
Show Answer
Answer:
Correct Answer: D
Solution:
[d] Units of k indicate that reaction I is of second order and reaction II is first order. For I reaction, $ {t_{1/2}}\propto 1/a $ first $ {t_{1/2}}=1,hr, $ second $ {t_{1/2}}=2hr $
$ [A]=1M\xrightarrow{1,hr}0.5M\xrightarrow{2,hr}0.25M $
$ [B]=1M\xrightarrow{1,hr}0.5M\xrightarrow{1,hr}0.25M\xrightarrow{1hr}0.125M $
$ \frac{[ A ]}{[ B ]}=\frac{0.25M}{0.125M}=2 $
