The first-order gas-phase reaction $A (g) 3 B (g)$ is studied at constant volume and temperature. The total pressure is 150 mmHg after 10 min, and 240 mmHg after complete reaction. Take $ln 10 = 2.303$ . The time (in min) for 90% of A to react is

Answer: B

From

P_{\infty} = 3 P_{0}

P_{0} = 80

mmHg. With

P_{t} = P_{0} + 2 x

x = 35

mmHg and

p_{A} = P_{0} - x = 45

mmHg.

k = \frac{1}{10} ln \frac{80}{45} = 0.0575 mi n^{- 1}

. For 90% conversion,

t = \frac{2.303}{k} = 40.0

min.