Question

At $518^{\circ} C$ , the rate of decomposition of sample of gaseous acetaldehyde, initially at a pressure of $363$ Torr, was $1. 00$ Torr $s^{-1}$ when $5\%$ had reacted and $0.5$ Torr $s^{-1}$ when $33\%$ had reacted. The order of the reaction is -

• A. 2
• B. 3
• C. 1
• D. 0

Answer 1

Answer: (A)

2

Answer 2

Assume the order of reaction with respect to acetaldehyde is $x$.

Rate $= k\, \left[ CH _{3} CHO \right]^{ x }$
$1= k \,[363 \times 0.95]^{ x }$
$1= k\, [344.85]^{ x }\,\,\,\,\,\,\,\,\,...(i)$
$0.5= k\, [363 \times 0.67]^{ x }$
$0.5= k \,[243.21]^{ x }\,\,\,\,\,\,\,...(ii)$

Divide equation (i) by (ii),

$\frac{1}{0.5}=\left(\frac{344.85}{243.21}\right)^{ x }$
$\Rightarrow 2=(1.414)^{ x }$
$\Rightarrow x =2$