Resources | Subject Notes | Physics
Evaporation is the process by which a liquid changes into a gas or vapour. This occurs when liquid molecules gain enough kinetic energy to overcome the intermolecular forces holding them together.
The rate of evaporation is directly proportional to the temperature of the liquid. Higher temperatures mean the liquid molecules have more kinetic energy. This increased kinetic energy allows more molecules to escape into the gaseous phase. The relationship can be represented as:
Rate of Evaporation ∝ Temperature
A higher temperature will lead to a faster rate of evaporation.
The rate of evaporation is directly proportional to the surface area of the liquid. A larger surface area provides more liquid molecules with the opportunity to escape into the gaseous phase.
Rate of Evaporation ∝ Surface Area
For example, a puddle will evaporate faster than the same volume of water in a deep container.
Air movement, particularly wind, affects the rate of evaporation by removing the vapour molecules from the surface of the liquid. This creates a lower concentration of vapour above the liquid, encouraging more liquid molecules to evaporate.
Humidity refers to the amount of water vapour already in the air. High humidity means the air is already close to saturation with water vapour, so evaporation will be slower. Low humidity means the air can absorb more water vapour, leading to faster evaporation.
Wind increases the rate of evaporation by removing water vapour from the immediate vicinity of the liquid.
| Factor | Effect on Evaporation Rate | Explanation |
|---|---|---|
| Temperature | Increases | Higher temperature = more kinetic energy = more molecules escape |
| Surface Area | Increases | Larger surface area = more molecules exposed = more escape opportunities |
| Air Movement (Wind) | Increases | Removes vapour from surface = lower vapour concentration = more evaporation |
| Humidity | Decreases | High humidity = air close to saturation = less evaporation |