Condensation is a physical process in which a gas or vapor changes into a liquid. This phase change usually occurs when vapor cools to its dew point, when pressure increases, or when the air becomes saturated or supersaturated with vapor. It is the reverse of vaporization. ^[1–3]

How Condensation Occurs

Condensation is a physical change, so the chemical composition of the substance does not change. For example, when water vapor condenses into liquid water, both forms still contain H₂O molecules. ^[1,2]

To understand condensation, it is beneficial to look at particle motion. In the gaseous state, particles have relatively high kinetic energy. They move freely and rapidly, remaining far apart, allowing gases to spread out and fill the available space.

When a gas or vapor cools, its particles lose kinetic energy and move more slowly. As their motion decreases, the particles come closer together. The attractive forces between them, called intermolecular forces, become more effective. These forces pull the particles close enough to form a liquid.

In the case of water, fast-moving water vapor molecules lose energy, slow down, and come together to form liquid water droplets.

Examples

Condensation is common in nature and everyday life. ^[3–5]

Energy Equation for Condensation

Condensation releases heat energy, so it is an exothermic process. The heat released during this phase change is called the latent heat of condensation. ^[1,2]

If Q represents the positive amount of heat released, then:

Q = mL

Where:

Q: Heat released

m: Mass of vapor that condenses

L: Specific latent heat of condensation, usually measured in J/kg

This equation shows that the heat released depends on both the mass of vapor that condenses and the specific latent heat of the substance. Also, the specific latent heat of condensation is equal in magnitude to the specific latent heat of vaporization for the reverse process under the same conditions.