The heat needed to turn a unit mass of liquid into vapor without changing its temperature is known as what?

The correct answer is the latent heat of evaporation. This term refers specifically to the quantity of heat required to convert a unit mass of liquid into vapor at a constant temperature and pressure. During this process, the liquid absorbs heat energy, which facilitates the transition from a liquid phase to a vapor phase, but does not increase the temperature of the substance itself.

This concept is crucial in thermodynamics and power engineering, as it plays a significant role in processes such as steam generation in boilers, where water must absorb a considerable amount of heat to become steam without increasing its temperature.

Sensible heat relates to temperature changes in a substance and is the heat that causes a change in temperature without a phase change. The boiling temperature refers to the specific temperature at which a liquid transitions to vapor, which does not involve a quantifiable heat measure like latent heat. Fusion energy, on the other hand, pertains to the heat absorbed or released during a phase change from solid to liquid and is unrelated to the conversion from liquid to vapor.