Condensation, the process of a gas turning into a liquid, releases heat. This fundamental physical change transfers energy to the surrounding environment. This energy release is a core principle in thermodynamics, affecting everything from global weather patterns to the moisture on a cold drinking glass. Condensation occurs when water vapor in the air cools down, transforming into liquid water droplets when it can no longer remain a gas.
The Concept of Latent Heat
The energy involved in this phase change is known as latent heat, or “hidden heat,” because it is transferred without causing an immediate change in the substance’s temperature. Latent heat is the energy absorbed or released when a substance changes its state, such as from a solid to a liquid, or from a gas to a liquid. This energy is not used to make the molecules move faster, but rather to change their arrangement and bonding.
The energy absorbed when liquid water turns into a gas through evaporation is called the latent heat of vaporization. Conversely, the same amount of energy must be released when that water vapor condenses back into a liquid; this is the latent heat of condensation. For water, this energy is substantial, requiring or releasing approximately 2,257 kilojoules for every kilogram of water that changes phase at its boiling point.
Why Condensation is an Exothermic Process
Condensation is classified as an exothermic process, meaning it releases energy into the environment. To understand why, it is helpful to look at the process on a molecular level. Water molecules in the gaseous state, or vapor, are highly energetic and move rapidly, with weak attractive forces between them.
For these gas molecules to become a liquid, they must slow down and move closer together, allowing strong intermolecular forces to form. The excess kinetic energy that kept the molecules separate must be shed for this transition to occur. This surplus energy is the heat released into the surroundings, enabling the molecules to settle into the lower-energy, more ordered state of a liquid.
The formation of new bonds between molecules causes the energy release. The heat released during condensation is equal to the heat that was initially absorbed during the opposing process of evaporation, following the principle of energy conservation.
Everyday Examples of Released Energy
The release of heat during condensation is a factor in many real-world phenomena. One example is the role of latent heat in powering large weather systems, such as thunderstorms and hurricanes. As warm, moist air rises and the water vapor condenses to form clouds, the massive amount of latent heat released warms the surrounding air.
This warming makes the air more buoyant, causing it to rise further and fueling the rapid vertical growth of storm clouds, intensifying the weather system. On a common scale, the formation of morning dew or fog involves the release of this heat, though the effect is usually too subtle to feel. When water vapor meets a cool surface, it condenses and releases a small amount of heat to that object.
A more direct example of this exothermic process is the severe burn caused by steam compared to boiling water at the same temperature. Both 100°C steam and 100°C boiling water are hot, but steam carries the additional, hidden energy of its latent heat. When 100°C steam touches the cooler surface of the skin, it instantly condenses into 100°C liquid water, releasing a large burst of latent heat directly onto the tissue. This additional energy transfer is why a steam burn is much more damaging than a burn from just hot water.