Entropy as a property: Is entropy a point function (state function) and therefore a thermodynamic property?

Introduction / Context:
Thermodynamic analysis distinguishes between properties (state functions) and path-dependent quantities. Correctly classifying entropy ensures proper application of the second law and allows use of property tables and charts independent of the process path taken between states.

Given Data / Assumptions:

• Closed or open systems can be considered.
• Entropy s is defined for equilibrium states.
• Processes may be reversible or irreversible, but states are equilibrium states.

Concept / Approach:
Entropy is a property: its differential is exact, and the change in entropy between two equilibrium states depends only on those states, not the path. Although δQ/T appears in the Clausius relation, entropy change can be evaluated for any process by integrating along a hypothetical reversible path between the same end states.

Step-by-Step Solution:

Verification / Alternative check:
Steam tables list entropy as a function s(T, p) or s(T, x) for water/steam, which is only meaningful because s is a property, independent of the actual process taken to reach that state.

Why Other Options Are Wrong:

• Incorrect / only for reversible / only for ideal gases: Entropy as a property is universal; reversibility affects how we compute Δs via heat interactions, not the property status.

Common Pitfalls:
Confusing the path-dependence of heat δQ with entropy; entropy change is computed via a reversible path even if the real process is irreversible.

Final Answer:
Correct