Question

For a reaction, $2NO+2H_2\to N_2+2H_{2}O$, the possible mechanism is
$2NO\rightleftharpoons N_2{O}_2$
$N_2{O}_2+H_2\stackrel{slow}{\to }{N}_{2}O+H_{2}O$
$N_{2}O+H_{2}O\stackrel{fast}{\to }{N}_2+H_{2}O$
What is the rate law and order of the reaction?

• A. $Rate=\left[N_2{O}_2\right],order=1$
• B. $Rate=\left[N_2{O}_2\right]\left[H_2\right],order=2$
• C. $Rate=[N_2{O}_2{]}^2,order=2$
• D. $Rate=\left[N_2{O}_2{]}^2\right[H_2],order=3$

Answer 1

Answer: (B)

$Rate=\left[N_2{O}_2\right]\left[H_2\right],order=2$

The slowest step of the reaction is rate determining step.
$N_2{O}_2+H_2\to N_{2}O+H_{2}O$
Rate of reaction $=\left[N_2{O}_2\right]\left[H_2\right]$
Hence, order of reaction $=2$.