The countless activities of everyday life are governed by the movement and transformation of energy. An electric oven takes energy from a power plant and gives it to a loaf of bread. A hammer transfers energy from arm muscles to a nail, and a falling object transforms potential energy into kinetic energy. Heat is perhaps the most familiar form of energy, and condensation is one of the countless natural phenomena that involve the movement of heat between an object and its surroundings.
Reactions that involve heat transfer fall into two general categories: endothermic and exothermic. These words denote a relationship between the objects involved in a reaction, known as the system, and the general environment in which the reaction takes place, known as the surroundings. An exothermic reaction releases heat into the surroundings, and an endothermic reaction absorbs heat from the surroundings. Frying an egg is an example of an endothermic process because the egg solidifies as it absorbs heat from the frying pan. A common example of an exothermic reaction is combustion in the form of a bonfire -- anyone near the flames can readily determine that the fire is releasing heat into the surroundings.
Most matter exists in three general forms: gas, liquid and solid. You routinely encounter water in all three forms. Solid water is called ice, liquid water is simply water, and gaseous water is known as vapor. Water vapor is present in the air you breathe, though you cannot see it. Condensation is the conversion of water vapor into a more condensed form, either liquid or solid, but in everyday language, condensation is the transformation of water vapor into liquid water. For example, water vapor in the air condenses into water droplets that appear on a glass filled with a cold beverage.
Molecules in Motion
Condensation is an exothermic process, but in contrast to a bonfire, condensation is not so obviously exothermic because it does not release heat in a way that is easy to sense or observe. Objects in motion have kinetic energy related to this motion, and water molecules are no exception. Liquid water becomes a gas when the molecules acquire enough kinetic energy to move freely despite the attractive forces that tend to keep molecules close together. This means that the molecules in water vapor are inherently more energetic than the molecules in liquid water. When water vapor turns into liquid water, this excess molecular energy cannot disappear, so it is released into the surroundings as heat.
Nature's Air Conditioner
The amount of heat released by common forms of condensation is small relative to the surrounding environment. This is why homeowners use the combustion of wood or propane, rather than condensation, to warm up a house. But you can get an idea for the thermal effects of condensation by considering the opposite phenomenon: evaporation, the conversion of liquid water into water vapor, which is a standard way to cool something down. Evaporation is endothermic because water molecules must absorb heat from the surroundings to increase their kinetic energy. One familiar example is sweat, which cools the human body as it evaporates from the skin.
- HyperPhysics: Energy Forms
- University of Minnesota: Endothermic and Exothermic Reactions
- Frostburg State University: What are Some Examples of Exothermic and Endothermic Processes?
- Purdue University: Condensation and Evaporation
- Glendale Community College: Thermochemistry
- Bakersfield College: Gases, Liquids and Solids
- Jupiterimages/liquidlibrary/Getty Images