Question 65

The Correct Answer is B **Explanation of Correctness (Option B):** Option B states that the vapor pressure increases with the temperature, which is chemically correct. Vapor pressure is the pressure exerted by the gas (vapor) phase of a substance in equilibrium with its solid or liquid phase in a closed container. As the temperature of a liquid increases: 1. **Kinetic Energy Rises:** The molecules gain more kinetic energy. 2. **Increased Escape Rate:** A larger fraction of molecules possess enough energy to overcome the intermolecular forces holding them in the liquid state and escape into the gas phase (evaporation). 3. **Higher Concentration of Vapor:** This leads to a greater concentration of vapor molecules above the liquid surface, resulting in more frequent collisions with the container walls. 4. **Increased Pressure:** Consequently, the measured pressure exerted by the vapor (the vapor pressure) increases. This relationship is governed by the Clausius-Clapeyron equation, which shows a positive, non-linear correlation between temperature and vapor pressure. **Explanation of Incorrect Options:** * **A) The pressure is not affected by temperature:** This is incorrect. Temperature is the primary factor affecting vapor pressure, as it determines the kinetic energy of the molecules and their ability to escape the liquid phase. * **C) The pressure may increase or decrease as the temperature rises:** This is incorrect. For any pure substance, vapor pressure is an intensive property that *always* increases systematically and predictably as the temperature increases, provided the substance remains below its critical point. * **D) The pressure decreases as temperature increases:** This is the opposite of the correct relationship and is incorrect. Raising the temperature promotes evaporation, thereby increasing the concentration of gas particles and increasing the pressure, not decreasing it.