Question

At 100°C the gaseous reaction A → 2B + C is found to be first order. On starting from pure A it is found that at the end of 10 min the total pressure of system is 176 mm of Hg. After a long time, pressure becomes 270 mm Hg. The partial pressure of A at the end of 10 min is (in mm of Hg)

(a)  43

(b)  47

(c)  94

(d)  86

Answer 1

Correct option   (b) 47

Explanation:

Since P ∝ no of moles, and after long time only B and C are formed A has completely disappeared, therefore pressure of 270 mm is for 3 moles of gaseous products. Hence pressure due to one mole = 270/3 = 90 mm

Hence initial pressure = 90 mm;

Pressure at 10 min = 176 = 90 – x + 2x + x or x = 43 mm

or pressure due to A at 10 min = 90 – 43 = 47 mm