Eduard-Job-Stiftung für Thermo- und Stoffdynamik

Entropieerzeugung in einem Entropiestrom

Isothermal Compression

A process is called isothermal, if the temperature of the system does not change. It is therefore possible to use the following simplification of the main equation (equation 1)

:   since dT = 0 by definition

Substituting p = nRTV -1 (ideal gas law) results in:

To obtain BOYLE's law from this equation dS needs to be replaced by an expression containing dp. Such an expression can be found by exploiting the corresponding reciprocity relation1 and applying to it the ideal gas law.

Substituting dS in the main equation yields


and by subsequent integration BOYLE's law is finally obtained.


  1. All reciprocity relations can be summarized in a single mathematical operation called turning of a differential quotient. G. Job; Z. Naturforsch. 25a 1970 1502 - 1508.