Question

At $500K$ , the half-life period of a gaseous reaction at an initial pressure of $80kPa$ is $350s$ . When the pressure is $40kPa$ , the half-life period is $175s$ . The order of the reaction is

• A. zero
• B. one
• C. two
• D. three
• E. half

Answer 1

Answer: (A)

$P_1=80kPa,(t_{1/2})=350s$
$P_2=40kPa,{(t_{1/2})}_2=175s$
$\frac{80}{40}=\frac{350}{175}=2$
$\because$ $\frac{P_1}{P_2}=\frac{{(t_{1/2})}_1}{{(t_{1/2})}_2}=\frac{a_1}{a_2}$
$\therefore$ $=t_{1/2}\propto a$ (zero order reaction)
Note: For $n^{th}$ order reaction $t_{1/2}\propto \frac{1}{{(a)}^{n-1}}$