Question

Liquid water turns to ice. Is this process endothermic or exothermic? Explain what is occurring using the terms system, surroundings, heat, potential energy, and kinetic energy in the discussion.

Short answer

The process of liquid water turning into ice is an exothermic process, as it releases heat to its surroundings. In this process, the system (liquid water) experiences an increase in potential energy due to more structured and stable hydrogen bonds forming in the ice lattice structure, while its kinetic energy decreases as water molecules slow down and lose energy.

Step-by-step solution

Identify the System and Surroundings

In this exercise, the system is the liquid water that is undergoing the phase change and turning into ice. The surroundings include everything outside the system, such as the container holding the water and the environment in which the process is occurring.

Determine Heat Transfer

When liquid water turns into ice, it releases heat to its surroundings. This is because the water molecules slow down and lose energy as they form the more ordered and structured solid ice. This heat transfer to the surroundings is known as an exothermic process.

Examine Potential Energy

During this phase change, the potential energy of the system increases. Potential energy refers to the stored energy in a substance based on its position or arrangement. In the case of liquid water turning to ice, the potential energy increases because the water molecules are moving closer together and forming more structured and stable hydrogen bonds in the ice lattice structure compared to the less structured arrangement of liquid water.

Examine Kinetic Energy

Kinetic energy refers to the energy of motion. In this process, the kinetic energy of the system decreases as the liquid water turns to ice. This is because the water molecules slow down and lose energy as they move closer together and form more stable bonds in the solid state. The decrease in kinetic energy within the system is partially responsible for the release of heat energy to the surroundings.

Endothermic or Exothermic Process

Based on the analysis of heat transfer, potential energy, and kinetic energy, we can conclude that the process of liquid water turning into ice is an exothermic process. This is because the system releases heat to the surroundings, the potential energy increases, and the kinetic energy decreases during the process.