If the temperature of a gas decreases, which of the following must also decrease for the gas to stay in equilibrium?

When the temperature of a gas decreases, the behavior of the gas can be explained by Charles' Law, which states that at constant pressure, the volume of a gas is directly proportional to its absolute temperature (in Kelvin). In simpler terms, if the temperature of a gas decreases, the volume must also decrease to maintain equilibrium, assuming that the pressure and the amount of gas (moles) are constant.

As temperature falls, the kinetic energy of the gas molecules decreases, leading to a reduction in the volume they occupy. If the volume did not decrease when the temperature does, then pressure would have to change, potentially causing the gas to be out of equilibrium.

This relationship holds true under ideal conditions, which help illustrate the fundamental principles outlined in the gas laws. Thus, for the gas to remain in a state of equilibrium with a decrease in temperature, the volume must also decrease.