Which statement correctly defines latent heat of vaporization Lv?

Which statement correctly defines latent heat of vaporization Lv?

• A. Lv is energy required to melt a solid.
• B. Lv is energy required to convert a liquid to gas at its boiling point.
• C. Lv is energy required to convert a gas to a liquid.
• D. Lv is energy required to raise the temperature without a phase change.

Answer: (B)

Latent heat of vaporization is the energy needed to turn a given amount of liquid into a gas at its boiling point, with the temperature staying the same. This energy goes into breaking intermolecular attractions so particles escape into the vapor phase, not into making them move faster. It’s usually measured per unit mass (like J/kg). This statement is the right one because it captures two key ideas: the phase change from liquid to gas, and the fact that the temperature does not rise during that change at the boiling point. The other options describe different ideas: melting a solid is latent heat of fusion, gas to liquid is condensation, and heating without a phase change is sensible heat.

Latent heat of vaporization is the energy needed to turn a given amount of liquid into a gas at its boiling point, with the temperature staying the same. This energy goes into breaking intermolecular attractions so particles escape into the vapor phase, not into making them move faster. It’s usually measured per unit mass (like J/kg).

This statement is the right one because it captures two key ideas: the phase change from liquid to gas, and the fact that the temperature does not rise during that change at the boiling point. The other options describe different ideas: melting a solid is latent heat of fusion, gas to liquid is condensation, and heating without a phase change is sensible heat.