Latentheat

Latent heat is the energy absorbed or released by a substance during a phase transition at a constant temperature. It describes the hidden energy involved in changing the structure of a material, rather than raising its temperature. During melting, boiling, or sublimation, heat is transferred without a change in the substance’s temperature until the phase change completes.

The main types are latent heat of fusion, latent heat of vaporization, and latent heat of sublimation. The corresponding specific latent heats are Lf, Lv, and Ls. The heat required to change the phase of a mass m is q = mLf for fusion, q = mLv for vaporization, and q = mLs for sublimation. For water at standard pressure, Lf is about 333 kJ/kg, Lv about 2257 kJ/kg, and Ls about 2834 kJ/kg.

Phase changes occur at specific temperatures—the melting point for fusion and the boiling point for vaporization—and the temperature remains constant during the transition. When the material is not undergoing a phase change, added heat changes its temperature (sensible heat) rather than its phase.

Latent heat is central to many natural and engineered processes. Ice melting absorbs heat, water boiling requires large energy input, and steam condensing releases heat. In meteorology, latent heat released by condensing water vapor powers atmospheric convection and storms. Latent heat is measured by calorimetry and is important in the design of heating, cooling, and food-processing systems.