The First Law of Thermodynamics and the Thermodynamic Description of Elastic Solids

TL;DR

This paper proposes a revised thermodynamic framework for elastic solids, challenging traditional assumptions, and derives equations that better match experimental data for MgO's internal energy.

Contribution

It introduces a new thermodynamic description for elastic solids, questioning existing principles like Joule's postulate, and derives equations that align well with experimental data.

Findings

New thermodynamic equations for elastic solids derived.

Good agreement with experimental data for MgO.

Challenges the universality of Joule's postulate.

Abstract

Historically, the thermodynamic behavior of gasses was described first and the derived equations were adapted to solids. It is suggested that the current thermodynamic description of solid phase is still incomplete because the isothermal work done on or by the system is not counted in the internal energy. It is also suggested that the isobaric work should not be deducted from the internal energy because the system does not do work when it expands. Further more it is suggested that Joule postulate regarding the mechanical equivalency of heat -the first law of thermodynamics- is not universal and not applicable to elastic solids. The equations for the proposed thermodynamic description of solids are derived and tested by calculating the internal energies of the system using the equation of state of MgO. The agreement with theory is good.