How does a decrease in volume affect the pressure of a gas in equilibrium?

When the volume of a gas in a closed system decreases, the particles of the gas become more confined within the smaller space. This leads to an increase in the frequency of collisions between gas particles and the walls of the container. As the collision rate increases, the pressure of the gas, defined as the force exerted by the gas particles against the walls of the container per unit area, also increases.

According to Boyle's Law, which states that pressure is inversely proportional to volume for a fixed amount of gas at a constant temperature, when volume decreases, pressure must increase, provided that the number of moles of gas and temperature remain constant.

In a scenario where the gas is part of a chemical equilibrium reaction, a change in volume would also affect the position of equilibrium according to Le Chatelier's principle. If the reaction involves a change in the number of moles of gas on the reactant and product sides, reducing the volume will shift the equilibrium in the direction which produces fewer moles of gas to counteract the change. However, the immediate effect of a decrease in volume is simply an increase in pressure.

Thus, the correct response is that a decrease in volume leads to an increase in pressure.