What is latent heat?
Latent heat is the name given to energy which is either lost or gained by a substance when it changes state, for example from gas to liquid. It is measured as an amount of energy, joules, rather than as a temperature. Most substances can exist in three states: gas, liquid and solid, though there is an additional state named plasma. The main difference between a substance in each state is how quickly its molecules are moving. As a liquid, the molecules move at a speed where they can repeatedly join together, break apart, then join together again. When they move slowly, they stay joined together, forming a solid. When they move quickly, they stay broken apart, forming a gas. For example, we usually think of water as a liquid. However, it can also be a solid (ice) or a gas (steam). But as you can see when you boil water in a kettle or when the surface of a pond freezes, not all of the molecules in a substance change state at the same time. When a molecule changes state, it has a different
Latent heat is the heat required to change water from the liquid phase to the gaseous phase. Vaporization can occur without change in temperature. For air-water mixtures, the temperature at which vaporization occurs depends on the vapor pressure of the water vapor. Vaporization occurs at 100C at a vapor pressure of 100 kPa and at 18C at a vapor pressure of 2 kPa. Latent heat is much larger than sensible heat. The latent heat of water is 2500 kJ/kg while the sensible heat of water is 4.2 kJ/(kg C). 600 times more heat is required to vaporize water than is required to raise its temperature by 1C. Or alternatively, another way of looking at this is that during condensation of water vapor into liquid, 600 times more heat is released compared to the amount of heat released when liquid water temperature is reduced by 1C. When water vapour in a rising air parcel condenses into liquid, latent heat is released. This has important implications for an atmospheric vortex engine since the release o
