Final answer:
Evaporation is the enthalpy of vaporization; it's an endothermic process where a liquid absorbs energy to become a gas. The energy absorbed during the conversion is always positive. Condensation, its exothermic counterpart, releases energy.
Step-by-step explanation:
The process of evaporation, where liquid transforms into gas and stores energy, is termed the enthalpy of vaporization (or heat of vaporization). This process can occur at temperatures below the boiling point of the liquid. Molecules near the surface of the liquid can absorb energy from the environment, allowing them to transition into the gas phase.
The enthalpy of vaporization is the amount of energy required for converting a liquid into a gas, which is always considered positive during this endothermic process. When a substance transitions from gas back to liquid, a process known as condensation, the energy involved is negative, indicating that it's exothermic and energy is released.
Vapor pressure is a related concept that arises when vaporization occurs in a closed environment, leading to equilibrium between the rates of evaporation and condensation. The measure of the pressure exerted by the vapor when it is in equilibrium with its liquid is known as the vapor pressure of the liquid.