What does the term "latent heat" refer to?

The term "latent heat" specifically refers to the heat absorbed or released by a substance during a phase change without a change in temperature. This can occur during processes such as melting, freezing, vaporization, or condensation. During these phase changes, the energy is utilized to alter the state of the substance (for example, from solid to liquid or liquid to gas), rather than to increase its thermal energy. This concept is crucial in HVAC/R systems, as it influences how heat is transferred in refrigerants and in various thermal processes, affecting overall efficiency and performance.

Other options, while related to heat, do not capture the essence of latent heat. The first option focuses on sensible heat, which is associated with temperature changes rather than phase changes. The third option mentions heat loss during condensation, which is a specific instance of latent heat but does not encompass the broader definition. Lastly, the fourth option refers to measurable heat by thermometers, which pertains to temperature rather than the energy involved in a phase change. Thus, understanding latent heat is essential for properly managing and manipulating thermal systems in HVAC/R applications.