A saturated vapour pressure of a liquid increases when the

Analysis of the Question

The question asks about the relationship between the Saturated Vapour Pressure (SVP) of a liquid and other physical factors. We need to identify which factor causes the SVP to rise.

Concept Explanation

Saturated Vapour Pressure (SVP) is the pressure exerted by a vapour when it is in dynamic equilibrium with its own liquid in a closed container.

1. Kinetic Theory: Molecules in a liquid are in constant motion. Some molecules near the surface have enough kinetic energy to escape into the space above the liquid (evaporation).
2. Temperature Effect: Temperature is a measure of the average kinetic energy of the molecules. When you increase the temperature, more molecules gain sufficient energy to overcome the intermolecular forces holding them in the liquid phase.
3. Equilibrium: As more molecules escape into the vapour phase, the pressure exerted by the vapour increases until a new equilibrium is reached at a higher pressure. Therefore, SVP is strictly a function of temperature.
4. Volume Independence: Changing the volume of the container or the volume of the liquid does not change the SVP. If you increase the volume of the container, more liquid will simply evaporate until the pressure returns to the original SVP for that specific temperature.

Step-by-Step Solution

• Step 1: Recognize that SVP is defined as the pressure of the vapour in equilibrium with the liquid at a specific temperature.
• Step 2: Recall the kinetic theory of matter: higher temperature = higher average kinetic energy = more molecules escaping the liquid surface.
• Step 3: Evaluate the options: • Option A: Increasing temperature increases the kinetic energy of molecules, leading to a higher rate of evaporation and thus a higher SVP. This is correct. • Option B & C: Changing the volume of the liquid or the container does not change the equilibrium pressure (SVP) at a constant temperature. • Option D: Decreasing the temperature reduces the kinetic energy of the molecules, which decreases the SVP.

Conclusion

The saturated vapour pressure of a liquid is directly dependent on temperature. As the temperature of the liquid increases, the saturated vapour pressure also increases.

Exam Tip: Always remember the phrase "SVP depends only on Temperature." If you see a question asking what affects SVP, ignore volume, surface area, or pressure changes—look for the temperature option!