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Why Does Temperature Influence Evaporation Rate?

The evaporation of a liquid is a familiar, everyday phenomenon. Around the home, you may be most familiar with the evaporation of water, but all types liquids can evaporate under the right conditions. Although evaporation from a bowl of soup may seem trivial, the process of evaporation is actually an essential component of the movement of water on the planet, or the water cycle.

Evaporation Process
- Evaporation is the process by which a liquid undergoes a phase change into a gas. Evaporation occurs only at the surface of a liquid and not throughout its volume, as with boiling. However, not every molecule at the liquid's surface can actually evaporate; the molecules that do so must possess certain characteristics and be able to overcome certain forces. Some liquids evaporate easily, while others evaporate at a negligible rate, meaning that some liquids can easily overcome the barriers to evaporation whereas others cannot.
Intermolecular Forces
- All of the molecules of a liquid interact with each other through intermolecular forces. How exactly the molecules interact depends on their chemical nature. For example, water molecules can interact through hydrogen boding, which produces relatively strong attractive forces, and therefore a greater effort is needed to separate them than molecules that cannot interact in such a way. The molecules in a liquid might interact only with each other if the liquid is pure, or they may interact with any other solute molecules also present.
Temperature
- A molecule can evaporate from the surface of a liquid if it can escape the intermolecular forces holding it back. In order to do so, it must have a sufficient amount of kinetic energy. The kinetic energy of the molecules in a liquid is proportional to the temperature and, as the temperature rises, so does the average kinetic energy of the molecules. As the molecules move around, collide and transfer energy between each other, some of them will end up with enough kinetic energy to overcome the intermolecular interactions with other molecules near the surface of the liquid and break free.
Other Factors
- The rate of evaporation depends on several other factors, too. If the surface area of the liquid increases, so does the evaporation rate, because there are now more molecules near or at the surface that are potentially able to escape. However, if the concentration of the liquid molecules is already high in the air above the liquid, then fewer will be able to further evaporate. The same holds true if the air is also saturated with other substances. If the air above a liquid circulates, more liquid will be able to evaporate, since the new air flowing in will be less saturated with evaporating molecules.

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