At $518^{\circ} \mathrm{C}$, the rate of decomposition of a sample of gaseous acetaldehyde, initially at a pressure of 363 Torr, was 1.00 Torr $\mathrm{s}^{-1}$ when $5 \%$ had reacted and 0.5 Torr $\mathrm{s}^{-1}$ when $33 \%$ had reacted. The order of the reaction is :

JEE Main · 2018 · 08 Apr 2018 · Offline · Chemical Kinetics

51 8^{\circ} C

, the rate of decomposition of a 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 :

Answer: (B)

Using the rate law

r = k [A]^{n}

at two instants, the acetaldehyde pressure is

363 \times 0.95 = 345

Torr when the rate is

1.00

Torr s

^{- 1}

and

363 \times 0.67 = 243

Torr when the rate is

0.5

Torr s

^{- 1}

. Dividing one rate by the other,

\frac{1.00}{0.5} = (\frac{345}{243})^{n}

, so

2 = (1.42)^{n}

, and taking logarithms gives

n \approx 2

, a second-order reaction.

JEE Main · 2018 · 08 Apr 2018 · Offline · Single correct option