What is Latent Heat?

Latent heat, the abbreviation of phase change latent heat, refers to the heat absorbed or released by a substance from one phase to another under isothermal and isostatic conditions. This is one of the characteristics of the object when the solid, liquid, gas three phases and the different solid phases change. Latent heat between solid and liquid is called heat of fusion (or heat of solidification), heat between liquid and gas is called heat of vaporization (or heat of condensation), and heat between solid and gas is called sublimation heat (or heat of condensation) .

Latent heat

Means constant at temperature

Latent heat of fusion

The energy absorbed by a substance from a solid state to a liquid state without changing its temperature.

First-order phase transition (see

A substance undergoes a phase change (state change), and the heat absorbed or emitted when the temperature does not change is called "latent heat". When a substance changes from low energy to high energy, it absorbs latent heat and vice versa. For example, part of the latent heat absorbed when a liquid boils is used to overcome intermolecular gravity, and the other part is used to resist during the expansion process

In the first-order phase transition, heat is absorbed or released, accompanied by a change in volume, but the temperature of the system does not change. The heat absorbed or released is called "

Technically, the latent heat of phase change of certain substances is often used to cool. Dry ice (solid carbon dioxide) can also be made by absorbing heat when liquid carbon dioxide is vaporized. The method is to store liquid carbon dioxide in a high-pressure steel pipe at room temperature, open the steel cylinder valve when in use, and the liquid carbon dioxide sprayed suddenly drops from a high pressure state to a normal pressure state, so that it quickly vaporizes and absorbs a large amount of vaporization heat. The vaporization of liquid carbon dioxide causes another part to cool and solidify to dry ice. The temperature is as low as -78 ° C, which can be collected in a container and used as a refrigerant. Because dry ice is convenient in manufacturing, transportation, and use, and has no side effects, it is widely used in food refrigeration and scientific research. Artificial precipitation is the use of dry ice to quickly sublimate in the unprecipitated cold clouds and absorb a large amount of heat, causing the ambient air temperature to drop sharply, so that water vapor condensation in the clouds and supercooled water droplets freeze to form ice crystals. In the warmer air, it will turn into raindrops and land on the ground ^[2] .