The Problem of Coordination: Entropy as a Physical Quantity in Classical Thermodynamics

The problem of coordination for thermodynamic entropy as a physical quantity is expressed in two related questions: 1) What counts as a measurement of entropy? 2) What is entropy? These issues are considered in this paper for thermodynamic properties of pure substances in classical thermodynamics. The conceptual model to define entropy in the second law of thermodynamics cannot be used directly to produce an ideal experiment related to real measurements. Thus, the solution of the problem of coordination for entropy is based on the tight integration of entropy with other thermodynamic properties in the formalism of classical thermodynamics. Therefore, the solution of the problem of coordination for entropy is related to the simultaneous solution of the problem of coordination for other thermodynamic quantities, such as heat capacity, internal energy, enthalpy, and the Gibbs energy.