Final answer:
The purpose of a movable piston in a closed system is to control pressure and maintain equilibrium, especially during temperature changes, by allowing the volume of the enclosed gas to adjust.
Step-by-step explanation:
In a closed system fitted with a movable piston, the purpose of the piston is to control pressure within the system. As temperature increases, the molecules with higher energy push out against the piston, which can move to accommodate changes in internal pressure and maintain equilibrium. If the external pressure is constant, the piston's movement alters the volume of the gas, following Boyle's Law where pressure is inversely proportional to volume. In an isothermal process, for instance, where temperature is kept constant, the piston balances internal pressure with external pressures, ensuring the system remains at equilibrium. The piston does not regulate temperature, determine volume, or manage concentration directly, but it is integral to the workings of a dynamic closed system where gases expand or contract in response to thermal energy changes.