Question

Assertion :Observed rate constant of the given reaction given below decreases with temperature.
$NO+NO\underset{K_b}{\stackrel{K_f}{\rightleftharpoons }}{N}_2{O}_2$
$N_2{O}_2+O_2\underset{slow}{\stackrel{K}{\to }}2N{O}_2$
$2NO+O_2\to 2N{O}_2$ Reason: $K_c$ of the reaction being exothermic and decrease in $K_c$ overweigh increase in K with increase in temperature.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
• C. Assertion is correct but Reason is incorrect.
• D. Assertion is incorrect but Reason is correct.

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.

Rate of reaction is given by :

$Rate=K\left[N_2{O}_2\right]\left[O_2\right]$

and $K_c=\frac{\left[N_2{O}_2\right]}{[NO{]}^2}$

$\therefore rate=K.K_c\left[NO{]}^2\right[O_2]$

$=K_{obs}\left[NO{]}^2\right[O_2]$

Option (A) is correct.