Question

For a reaction $2NO + 2H_{2} \rightarrow N_{2} + 2H_{2}O$ the possible mechanism is

$2NO$ $N_{2}O_{2}$

$N_{2}O_{2} + H_{2}\overset{\quad Slow\quad}{\rightarrow}N_{2}O + H_{2}O$

$N_{2}O + H_{2}O\overset{\quad Fast\quad}{\rightarrow}N_{2} + H_{2}O$

What is the rate law and order of the reaction?

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

Answer 1

Answer: (B)

Rate = $\lbrack N_{2}O_{2}\rbrack\lbrack H_{2}\rbrack,$ order = 2

Answer 2

The slowest step of the reaction is the rate determining step.

$N_{2}O_{2} + H_{2} \rightarrow N_{2}O + H_{2}O$

Rate of reaction $= \lbrack N_{2}O_{2}\rbrack\lbrack H_{2}\rbrack$

Hence, order of reaction = 2