Thermodynamic equilibrium in stressed systems V. Reversible and irreversible processes

Abstract

It is shown that reversible and irreversible applications of force fields to systems can be treated rigorously using the entropy function S. For the reversible application of a force field to a system it emerges that the Gibbs criterion of equilibrium for reversible processes, (dS) u ≤ 0, may be applied to stressed systems, where dS is the entropy variation of the system as it is stressed, U is the internal energy of the system, and subscript U denotes dU=0 during the application of the force field. The results are applied to the physical adsorption of geses on solids. A method for determining a function W_F is given: W_F is defined as the work of induction of stress in the surface of an inert solid due to perturbation of the solid surface by an adsorbed gas, and is called the chemical work function.

For the irreversible application of a force field it emerges that the production of entropy, dS ₁0, may be used in describing stressed systems, where subscript i denotes irreversible process. The results are applied to rheology and to chemisorption. In the isothermal application (at temperature T) of a mechanical force field by the surroundings to a system, denoted, respectively, by superscripts α and β, in which work W is done, the following equation is derived: TdS _i ^α= TdS _p ^β + dW _p ^β+dW _i ^β

where subscript p denotes a quantity arising as a result of strain, the time parameter in the constitutive rheological equations of state being eliminated in their thormodynamic analogues. The determination of W _F.1 in chemisorption processes is considered.

For any reversible and irreversible isothermal cycle in which a system is strained by a force field, the following equation is derived: φ_st d(S _p+S _m)=0.

where φ_st denotes any isothermal strain cycle, and subscript m denotes a quantity arising as a result of mechanical equilibrium.