Which term refers to the energy required to convert a liquid to a gas at its boiling point?

Which term refers to the energy required to convert a liquid to a gas at its boiling point?

• A. Heat
• B. Light
• C. Latent Heat of Vaporization
• D. Hydrogen Bond

Answer: (C)

This question tests understanding of the energy required for a phase change from liquid to gas at the boiling point, which is the latent heat of vaporization. When a liquid reaches its boiling point, energy must be supplied to overcome the intermolecular forces holding the liquid together so that molecules can escape into the gas phase. This energy goes into changing the state, not raising the temperature, so the temperature stays constant while vaporization occurs. The amount of energy needed per unit mass or per mole is called the latent heat of vaporization, and it is specific to the substance (for water at 1 atm it’s about 40.7 kJ per mole or ~2257 J per gram). The other terms don’t describe this phase-change energy. Heat is a general term for energy transfer due to a temperature difference and can involve a temperature rise as well as phase change. Light is electromagnetic energy with no necessary relation to phase changes. Hydrogen bonds are a type of intermolecular attraction that contribute to the energy required to vaporize, but the specific term for the energy involved during vaporization is latent heat of vaporization.

This question tests understanding of the energy required for a phase change from liquid to gas at the boiling point, which is the latent heat of vaporization. When a liquid reaches its boiling point, energy must be supplied to overcome the intermolecular forces holding the liquid together so that molecules can escape into the gas phase. This energy goes into changing the state, not raising the temperature, so the temperature stays constant while vaporization occurs. The amount of energy needed per unit mass or per mole is called the latent heat of vaporization, and it is specific to the substance (for water at 1 atm it’s about 40.7 kJ per mole or ~2257 J per gram).

The other terms don’t describe this phase-change energy. Heat is a general term for energy transfer due to a temperature difference and can involve a temperature rise as well as phase change. Light is electromagnetic energy with no necessary relation to phase changes. Hydrogen bonds are a type of intermolecular attraction that contribute to the energy required to vaporize, but the specific term for the energy involved during vaporization is latent heat of vaporization.