Question

What do you understand by order of reaction? Give three examples of first order of reactions.

Answer 1

Order of Reaction: Sum of powers of active mass of reactants in rate law expression is called order of reaction. It is an experimental value which depends on state of experiment. Say following reaction occurs.
$mA+nB\to$ Product
Rate of reaction $=k{\left[A\right]}^m{\left[B\right]}^n$
Order of reaction $=m+n$
Hence, order of reaction is equal is $(m+n)$. In this reaction $m$ and $n$ are order of reaction with respect to $A$ and $B$ while total order of reaction is $m+n$. If sum of powers is equal to one, order of reaction is one. Example,
$N{H}_{4}N{O}_2\to N_2+2H_{2}O$
Rate of reaction $\propto {\left[N{H}_{4}N{O}_2\right]}^1$
Rate $=k{\left[N{H}_{4}N{O}_2\right]}^1$
Order of reaction $=1$
Example:
(1) Thermal dissociation of nitrogen pentaoxide.
(2) Hydrolysis of ester.
(3) $H_2{O}_2\underset{}{\overset{P+}{\to }}{H}_{2}O+\frac{1}{2}{O}_2$