Question

For a reaction, $2NO + 2H_{2} \to N_{2} + 2H_{2}O$, the possible mechanism is
$2NO {\rightleftharpoons} N_{2}O_{2}$
$N_{2}O_{2}+H_{2} \xrightarrow{\text{slow}} N_{2}O+H_{2}O$
$N_{2}O+H_{2}O \xrightarrow{\text{fast}} N_{2}+H_{2}O$
What is the rate law and order of the reaction?

• A. Rate $= [N_{2}O_{2}]$, order $= 1$
• B. Rate $= [N_{2}O_{2}] [H_{2}]$, order $= 2$
• C. Rate $= [N_{2}O_{2}]^{2}$, order $= 2$
• D. Rate $= [N_{2}O_{2}]^{2} [H_{2}]$, order $= 3$

Answer 1

Answer: (B)

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 $= [N_{2}O_{2}] [H_{2}]$
Hence, order of reaction $= 2$