The decomposition of a compound 'P' at temperature T, according to the equation: 2P(g) → 4Q(g) + R(g) + S(l) is a first-order reaction. After 30 min, from the start of the decomposition in a closed ve

Question

The decomposition of a compound 'P' at temperature T, according to the equation: 2P(g) → 4Q(g) + R(g) + S(l) is a first-order reaction. After 30 min, from the start of the decomposition in a closed vessel, the total pressure developed is found to be 445 mm and after a long time, total pressure is 625 mm. The vapour pressure of S(l) at this temperature is 25 mm. The total pressure after 60 min is

Prashant Kotian · Accepted Answer

Correct answer: 0535. Let initial P be P0. P_inf = (5/2)P0 + 25 = 625 => P0 = 240. At t=30, P_total = P_P + P_Q + P_R + 25 = (240 - 2x) + 4x + x + 25 = 240 + 3x + 25 = 445 => 3x = 180 => 2x = 120. Remaining P = 240 - 120 = 120. This is exactly half of P0, so t1/2 = 30 min. At 60 min (2 half-lives), remaining P = 60, so 2x = 180 and 3x = 270. P_total = 240 + 270 + 25 = 535 mm. Therefore, correct answer is 0535.

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