In order to determine the order of reaction: A(g) → 2B(g), vapour density of the system is determined at different stages of reaction, at constant temperature. The reaction is started with pure A(g).

Question

In order to determine the order of reaction: A(g) → 2B(g), vapour density of the system is determined at different stages of reaction, at constant temperature. The reaction is started with pure A(g). From the following data, the order of reaction is
Time (min): 0, 10, 20
Vapour density: 42, 35, 30

Prashant Kotian · Accepted Answer

Correct answer: 0. Total moles = 1 + α = VD_initial / VD_t. At t=0, α=0. At t=10, 1+α = 42/35 = 1.2 => α=0.2 (A remaining = 0.8). At t=20, 1+α = 42/30 = 1.4 => α=0.4 (A remaining = 0.6). The concentration of A decreases linearly with time (1.0 → 0.8 → 0.6), which characterizes a zero-order reaction. Therefore, correct answer is 0.

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