Question

An open ended mercury manometer is used to measure the pressure exerted exerted by a trapped gas as shown in the figure. Initially manometer shows no difference in mercury level in both columns as shown in diagram.After sparking 'A' dissociates according to following reaction $2A\left(g\right)\to 3B\left(g\right)+2C\left(g\right)$ If pressure of Gas "A" decreases to 0.8 atm. Then ( Assume temperature to be constant and is 300 K )

• A. total pressure increased by 1.3 atm
• B. total pressure increased by 0.3 atm
• C. total pressure increased by 22.3 cm of Hg
• D. difference in mercury level is 228 mm

Answer 1

Answer: (B), (D)

The correct options are
B total pressure increased by 0.3 atm
D difference in mercury level is 228 mm

Initial pressure of A is equal to atmospheric pressure which is 760 mm Hg.
At equilibrium, the pressures of A, B and C are 0.8,0.3 and 0.2 atm respectively.
The total pressure at equilibrium is $0.8+0.3+0.2=1.3atm$.
Thus the total pressure increased by 0.3 atm.
This corresponds to $0.3\times 760mm=228mmHg$.