Latent heat of vaporization is defined as which of the following?

• A. The rate of heat transfer in a conductor
• B. Heat released when water freezes
• C. The amount of heat required to raise the temperature of a gas
• D. The amount of heat needed to convert a liquid into a vapor

Answer: (D)

Latent heat of vaporization is the energy required to change a liquid into a vapor at a constant temperature and pressure. This energy goes into overcoming the attractive forces between molecules so they can spread apart as a gas, without raising the liquid’s temperature. In other words, it’s the amount of heat absorbed during the phase change from liquid to vapor.

For example, water requires about 2260 kJ of energy per kilogram to vaporize at 100°C, illustrating how much energy is needed to break intermolecular bonds during vaporization.

The other ideas don’t fit because they describe different concepts: heat transfer rate in a conductor is about how quickly heat moves, not about phase change; heat released when water freezes is latent heat of fusion (a release of heat during a solidification, not vaporization); and the heat to raise the temperature of a gas is sensible heat, which changes temperature without a phase change.