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Difficulty: MediumVapour Pressure, Boiling, Evaporation, and Relative Humidity

At a constant temperature, doubling the volume of a sealed container holding a liquid and its saturated vapour will cause the saturated vapour pressure to be halved.

Answer: Answer

Answer

The statement is false. Saturated vapour pressure depends exclusively on temperature and is independent of the container volume.
Saturated vapour pressure is entirely independent of the volume of the space occupied by the vapour. As long as liquid remains in the container to evaporate, expanding the volume simply causes more liquid to evaporate until the vapour pressure reaches its equilibrium saturation value at that temperature.

Step-by-Step Solution

1
Analyze the physical state of a saturated vapour in contact with its liquid.
A saturated vapour exists in dynamic equilibrium with its liquid phase, meaning the rate of evaporation equals the rate of condensation at that specific temperature.
Dynamic equilibrium determines the equilibrium vapour pressure above a liquid surface.
2
Examine the effect of increasing the container volume at constant temperature.
Expanding the volume temporarily reduces vapour concentration, causing the rate of evaporation to exceed condensation until the space is re-saturated.
Phase change allows the mass of the gas phase to change, unlike in closed ideal gas systems.
3
Conclude the value of the final vapour pressure.
The pressure returns to the exact same saturated vapour pressure (SVP) value as before the expansion.
SVP is an intrinsic property dependent only on temperature and the identity of the liquid, independent of volume.

Key Concept

Independence of Saturated Vapour Pressure from Volume
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Topics

Vapour Pressure, Boiling, Evaporation, and Relative Humidity

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