Question

The decomposition of gaseous acetaldehyde at $T(K)$ follows second order kinetics. The half-life of this reaction is $400\, s$ when initial pressure is $250$ torr. What will be the rate constant (in torr) and half-life (in s) respectively, if the initial pressure of acetaldehyde is $200$ torr at the same temperature?

• A. $10^5 $ and $500 $
• B. $10^{-5} $ and $400 $
• C. $10^{-4} $ and $400 $
• D. $10^{-5} $ and $500$

Answer 1

Answer: (D)

For $2^{nd} $ order reaction, $ k = \frac {1}{t_{1/2}p^{\circ}} $
where $ P^\circ $ is initial pressure
so $k = \frac{1}{400 \times 250} = 10^{-5} torr^{-1} sec ^{-1} $
when $P^ \circ = 200\, torr $