Chemical and Materials Sciences: Research Findings Vol. 9

Classical chemical thermodynamics remains the interpretive backbone of physical chemistry, chemical engineering, geochemistry and materials science, yet the discipline continues to carry unresolved conceptual and operational tensions that are rarely examined together. This review critically evaluates the core principles of the classical framework and the thermodynamic functions built upon them, tracing how foundational statements of the laws, the interpretation of entropy, the Legendre structure of the state functions, the practices of measurement and data evaluation, and the predictive models derived from them either reinforce or undermine one another. Literature was identified through open scholarly indexes and citation searching, appraised for methodological adequacy and conceptual contribution rather than citation count alone, and synthesised thematically around mechanisms, controversies and methodological weaknesses. Five findings emerge. Axiomatic reconstructions have clarified what the second law does and does not assert, but the version of the law transmitted through chemical practice remains logically weaker than the version defended in the foundational literature. Entropy is supported by several mutually incompatible interpretations, and the disagreement is substantive rather than merely verbal, as the long-running dispute over system entropy against total entropy demonstrates. The thermodynamic functions are formally secure yet operationally ambiguous, with standard states, activity conventions and the reaction Gibbs energy repeatedly misapplied in both research and instructional settings. Numerical thermodynamics depends on measurement and data-evaluation practices whose uncertainty structure is frequently under-reported, weakening the apparent precision of derived quantities. The boundaries of the classical framework, at small system sizes, under strong fluctuations and far from equilibrium, are now well characterised, but their implications for routine chemical practice remain largely unabsorbed. Confidence is strongest for the formal structure and the metrological foundations, and weakest for interpretive claims about entropy and for the transferability of classical reasoning to nanoscale and driven chemical systems.