Question

The concentration of $R$ in the reaction $R\to P$ was measured as a function of time and the following data is obtained:

[R] (molar)	1.0	0.75	0.40	0.10
t (min.)	0.0	0.05	0.12	0.18

The order of the reaction is:

• A. 0
• B. 1
• C. 2
• D. 3

Answer 1

The correct option is A 0

From two data, (for zero order kinetics)

$-\frac{dc}{dt}$ after 0.05 min $=\frac{0.25}{0.05}=5Mmi{n}^{-1}$
$-\frac{dc}{dt}$ after 0.12 min $=\frac{0.60}{0.12}=5Mmi{n}^{-1}$
$-\frac{dc}{dt}$ after 0.18 min $=\frac{0.90}{0.18}=5Mmi{n}^{-1}$
The average rate remains same throughout. This implies that rate is independent of concentration (zero order).