Question

Which of the following statement is correct for vapor pressure?

• A. Vapor pressure decreases with increase in temperature
• B. Vapor pressure is independent of temperature
• C. Vapor pressure increases with increase in temperature
• D. Vapor pressure becomes zero at high temperature

Hint:

Important facts about vapor pressure:
• Higher temperature \(\Rightarrow\) Higher vapor pressure
• Weak intermolecular forces \(\Rightarrow\) Higher vapor pressure
• Strong intermolecular forces \(\Rightarrow\) Lower vapor pressure Liquids like ether and acetone have high vapor pressure because their intermolecular forces are weak.

Answer 1

The Correct Option is C

Concept: Vapor pressure is the pressure exerted by the vapor of a liquid when the vapor and liquid are in dynamic equilibrium inside a closed container. At the surface of a liquid:
• Some molecules escape from the liquid phase into the vapor phase.
• Some vapor molecules return back to the liquid phase. When the rate of evaporation becomes equal to the rate of condensation, equilibrium is established and the pressure exerted by vapor molecules is called vapor pressure.

Step 1: Understanding the effect of temperature on molecular motion.
Temperature is directly related to the kinetic energy of molecules. When temperature increases:
• Molecules gain more kinetic energy.
• A larger number of molecules acquire enough energy to escape from the liquid surface.
• Evaporation increases. As more molecules enter the vapor phase, the pressure exerted by vapor molecules also increases.

Step 2: Relating temperature with vapor pressure.
Thus, \[ \text{Increase in temperature} \Rightarrow \text{Increase in vapor pressure} \] This is why liquids evaporate faster at higher temperatures.

Step 3: Analyzing the given options.

• Vapor pressure decreases with increase in temperature: Incorrect.
• Vapor pressure is independent of temperature: Incorrect because vapor pressure strongly depends on temperature.
• Vapor pressure increases with increase in temperature: Correct statement.
• Vapor pressure becomes zero at high temperature: Incorrect because vapor pressure actually becomes very high at high temperatures.

Step 4: Final conclusion.
Therefore, the correct statement is: \[ \boxed{\text{Vapor pressure increases with increase in temperature}} \] Hence, the correct option is: \[ \boxed{(3)\ \text{Vapor pressure increases with increase in temperature}} \]