Question

Vapour is injected at a uniform rate in a closed vessel which was initially evacuated. The pressure in the vessel

• A. increases continuously.
• B. decreases continuously.
• C. first increases and then decreases.
• D. first increases and then becomes constant.

Answer 1

Answer: (D)

first increases and then becomes constant.

Answer 2

Initially, as vapor is injected into the evacuated vessel, the number of molecules increases, leading to a continuous rise in pressure. As more vapor accumulates, the rate of condensation starts to match the rate of evaporation. When these rates become equal, a state of dynamic equilibrium is reached. At equilibrium, the vapor is saturated, and the pressure remains constant at the saturated vapor pressure for the prevailing temperature.