The term for the condition where a reversible process has no net change in macroscopic properties over time.

• A. Phase
• B. Phase Diagram
• C. Equilibrium
• D. Phase Boundaries

Answer: (C)

Equilibrium is the state in which a system’s macroscopic properties—such as composition, pressure, temperature, and phase distribution—remain constant in time. In a reversible process, forward and backward transformations occur at the same rate, so there is no net change in these properties as time progresses. This balance means the system can be described by constant observable values even though microscopic processes continue. For example, at chemical equilibrium the forward and reverse reaction rates are equal, giving constant concentrations. Phase concepts like a phase, phase diagram, or phase boundaries describe forms or maps of states, not the dynamic balance that keeps macroscopic properties constant over time.