JEE Main · 2020 · Shift-IIhardCK-013

For the reaction 2H2(g) + 2NO(g) N2(g) + 2H2O(g), the observed rate expression is: rate = kf[NO]2[H2]. The rate…

Chemical Kinetics · Class 12 · JEE Main Previous Year Question

Question

For the reaction $\mathrm{2H_2(g) + 2NO(g) \rightarrow N_2(g) + 2H_2O(g)}$ , the observed rate expression is: $\text{rate} = k_f[\mathrm{NO}]^2[\mathrm{H_2}]$ . The rate expression for the reverse reaction is:

Options

a
$k_b[\mathrm{N_2}][\mathrm{H_2O}]^2$
b
$k_b[\mathrm{N_2}][\mathrm{H_2O}]^2/[\mathrm{NO}]$
c
$k_b[\mathrm{N_2}][\mathrm{H_2O}]$
d
$k_b[\mathrm{N_2}][\mathrm{H_2O}]^2/[\mathrm{H_2}]$
✓

Correct Answerd

$k_b[\mathrm{N_2}][\mathrm{H_2O}]^2/[\mathrm{H_2}]$

Detailed Solution

At equilibrium: $r_f = r_b$

$k_f[\mathrm{NO}]^2[\mathrm{H_2}] = k_b \times r_b$

The equilibrium constant: $K_c = \frac{k_f}{k_b} = \frac{[\mathrm{N_2}][\mathrm{H_2O}]^2}{[\mathrm{NO}]^2[\mathrm{H_2}]^2}$

So: $k_f[\mathrm{NO}]^2[\mathrm{H_2}] = k_b \cdot \frac{[\mathrm{N_2}][\mathrm{H_2O}]^2}{[\mathrm{H_2}]}$

Therefore: $r_b = k_b\frac{[\mathrm{N_2}][\mathrm{H_2O}]^2}{[\mathrm{H_2}]}$

Answer: Option (4)

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