What happens to the pressure of water in a closed container when it is heated?

When water in a closed container is heated, the pressure increases due to several fundamental principles of thermodynamics. As the water temperature rises, the kinetic energy of the water molecules increases, causing them to move more vigorously. In a closed container, these fast-moving molecules collide with the walls of the container more frequently and with greater force.

This increased molecular activity leads to a rise in pressure. The molecules are confined, so as their movement escalates, the exertion of force against the container's walls amplifies, thus raising the overall pressure inside the container. This phenomenon is also described by Gay-Lussac's law, which states that the pressure of a gas is directly proportional to its temperature when the volume is held constant, and it applies to the gas phase of water (water vapor), as well as to the liquid phase under certain conditions.

Therefore, heating water in a closed system results in an increase in pressure due to the increased kinetic energy and subsequent molecular activity, making the correct response that the pressure increases.