Condensation is a phase transition where a substance shifts from a gaseous or vapor state into a liquid state. This process is the opposite of evaporation or boiling. It is frequently observed with water, such as when vapor cools and changes into liquid droplets, forming clouds or dew. As a change of state, condensation is governed by thermodynamics, making the involvement of energy unavoidable.
Energy States and Phase Change
Molecules in a gaseous state possess significantly higher kinetic energy than those in a liquid state. Gas molecules move rapidly and randomly, overcoming weak attractive forces and allowing them to spread out. In contrast, liquid molecules are closer together, held by stronger intermolecular forces that maintain a fixed volume while allowing the substance to flow.
For a gas to condense, the fast-moving molecules must slow down, allowing intermolecular forces to pull them together. This reduction in molecular speed corresponds directly to a loss of kinetic energy. The excess energy must be shed for the substance to transition to the lower-energy liquid phase, which is a prerequisite for forming liquid bonds.
The Release of Latent Heat
The process of condensation is classified as exothermic, meaning that energy is released into the surrounding environment as the substance changes state. This specific energy released is known as the latent heat of condensation. The term “latent” indicates that this energy transfer occurs without a change in the substance’s temperature, distinguishing it from sensible heat, which would cause a temperature change.
When water vapor condenses, the energy released is numerically equal to the energy absorbed during evaporation, known as the latent heat of vaporization. This substantial energy must be given off to the surroundings for the water molecules to settle into the liquid configuration. For water, the latent heat of condensation is approximately 2,260 Joules for every gram of vapor that condenses at 100°C.
The mechanism involves forming new intermolecular bonds, such as hydrogen bonds in water. Since the liquid state has lower potential energy than the gaseous state, the excess potential energy must be discharged as heat into the environment. This energy transfer facilitates the phase change without altering the temperature of the condensing vapor.
Practical Manifestations of Exothermic Energy
The release of latent heat has several observable effects in the everyday world and in large-scale natural systems. A powerful demonstration is the severity of a burn caused by steam at 100°C compared to liquid water at the same temperature. When steam contacts cooler skin, it instantly condenses, releasing its massive store of latent heat directly onto the tissue, compounding the burn caused by the high temperature alone.
In the atmosphere, condensation into cloud droplets is a major heating mechanism. As clouds form, the released latent heat warms the surrounding air, making it less dense and promoting convective uplift. This process fuels the intensification of weather systems, such as thunderstorms and tropical cyclones, driving atmospheric circulation globally.
A common household example is the fogging of a bathroom mirror during a hot shower. The warm, humid air meets the mirror’s cooler surface, causing water vapor to condense into liquid droplets. The heat released by this condensation slightly warms the air layer next to the mirror, demonstrating the same exothermic principle seen in global weather.