Question

Use the kinetic molecular theory to explain why a liquid gets cooler as it evaporates from an insulated container.

Short answer

During evaporation from an insulated container, high-energy molecules at the liquid's surface escape into the gas phase, taking energy from the remaining liquid. This causes a decrease in the average kinetic energy of the remaining liquid particles and a reduction in the liquid's temperature, resulting in the liquid becoming cooler. This phenomenon can be explained using the kinetic molecular theory, which states that particles in liquids are in constant random motion, exchanging energy through collisions.

Step-by-step solution

Understanding Kinetic Molecular Theory of Liquids

Kinetic molecular theory is a model that describes the behavior of liquids and gases on a molecular level. According to this theory, the particles (atoms or molecules) in liquids are in constant random motion. The motion of these particles makes them collide with one another and with the walls of the container in which the liquid is confined. As a result of these collisions, the particles exchange energy. Some particles will gain energy while others will lose energy.

Evaporation Process

Evaporation is the process in which the molecules at the surface of a liquid are converted from the liquid phase to the gas phase. Molecules in a liquid have a range of kinetic energies; some molecules have high energy while others have low energy. When a liquid is exposed to an external environment, the high-energy molecules at the surface have enough energy to escape the liquid phase and enter the gas phase. This process requires energy, which the escaping molecules acquire from the surrounding liquid.

Why a Liquid Gets Cooler During Evaporation

When high-energy molecules escape into the gas phase, they take some energy from the remaining liquid. Since this energy is being removed from the liquid, the average kinetic energy of the remaining particles decreases. As a result, the temperature of the liquid drops, and it gets cooler. To summarize, during evaporation from an insulated container, the high-energy molecules at the surface of the liquid escape into the gas phase, taking some energy from the liquid. This results in a decrease in the average kinetic energy of the remaining liquid particles and a drop in the temperature of the liquid, making it cooler.