23. ISO 80000-5 — Thermodynamics🔗

The third part specified in full is ISO 80000-5, Thermodynamics. Every item — all of 5-1 … 5-36, including every sub-suffixed item (5-3.1 … 5-3.3, 5-5.1/5-5.2, 5-6.1/5-6.2, 5-10.1/5-10.2, 5-16.1 … 5-16.4, 5-17.1/5-17.2, 5-20.1 … 5-20.5, 5-21.1 … 5-21.5, 5-25.1/5-25.2) — is catalogued: the temperatures, the expansion and pressure coefficients, heat and the heat-transfer quantities, the heat capacities and entropy, the energy family (the thermodynamic potentials), the specific energies, the Massieu and Planck functions, efficiency, and the humidity quantities — each carrying its exact source as data: the part, the printed item designation, the principal quantity symbol, and the coherent SI unit symbol. Only citation locators are recorded; no normative content (definitions, remarks) from the licensed standard is reproduced. The defining mathematics of selected remarks is formalized in the sibling module Part5.DefiningRelations.

Thermodynamics brings the one axis Parts 3 and 4 could not show, and sharpens the two the calculus already pressed. It introduces the temperature base quantity Θ, and with it the scale-type distinction — thermodynamic temperature is ratio-scale, but Celsius temperature, of the very same dimension, is only interval-scale (requirement R6, here on the standard). It holds the textbook entropy-versus-heat-capacity dimension collision (both J/K, down to the same unit string). And item 5-20 lays out the thermodynamic potentials — internal energy, enthalpy, the Helmholtz and Gibbs energies — as a specialization lattice over energy, mirroring Part 3's length family and Part 4's force family.