What is defined as "latent heat"?

Latent heat refers specifically to the amount of heat energy absorbed or released by a substance during a phase change, such as from solid to liquid (melting) or from liquid to gas (vaporization), without a change in temperature. This concept is crucial in thermodynamics and power engineering because it plays a key role in understanding energy transfers in systems involving various states of matter.

For example, when water boils, it requires a considerable amount of energy to convert from liquid to vapor. This energy does not raise the temperature of the water during the phase change; instead, it is used to break the molecular bonds holding the liquid together. Similarly, when ice melts, it absorbs heat, which facilitates the transition from solid to liquid without a temperature rise until all ice has melted.

In contrast, the other options either refer to specific types or conditions related to heat but do not capture the essential characteristic of latent heat. Latent heat is unique because it is associated with changes in state, whereas the other options do not encompass this critical aspect of energy transfer.