Ideal gas interaction with thermal radiation in classical thermodynamics and Gibb's paradox

摘要

The standard theory of ideal gases ignores the interaction of the gas particles with the thermal radiation (photon gas) that fills the otherwise vacuum space between them. Although acceptable in most cases, this feature of the theory contrasts with the evidence that all real materials, and hence in particular the particles of a real gas, absorb and radiate thermal energy. The interaction with the thermal radiation contained in the volume of a body may be important in gases. The latter, unlike solids and liquids, are capable of undergoing conspicuous volume changes, which entails large variations in the total amount of radiation that fills their volume in thermal equilibrium conditions. The paper considers a nonstandard ideal gas that differs from the classical one because it interacts with thermal radiation. This interaction is shown to produce temperature changes both in the free expansion of the gas and in its adiabatic mixing with another gas. Taking this kind of interaction into account also avoids the well-known Gibbs' paradox still keeping the theory within the realm of classical macroscopic thermodynamics, i.e. without resorting to the current statistical mechanics explanation.