First order gas phase reaction A B + C pi = initial pressure of gas A, pt = total pressure of the reaction mixture at time t Expression of rate constant (k) is
- 1t pi2pi - pt
- 1t 2pipi - pt
- 1t pi3pi - 2pt
- 1t 3pi4pi - pt
Answer
(1) 1t pi2pi - pt
Solution
Let the pressure of A decrease by x at time t:
A(g) B(g) + C(g)
t = 0: pi, 0, 0
t: pi - x, x, x
⇒ pt = (pi - x) + x + x = pi + x ⇒ x = pt - pi
⇒ pA = pi - x = 2pi - pt
For a first order reaction, k = 1t pipA
∴ k = 1t pi2pi - pt
Answer: (1)