Irreversible Processes

Abstract

Each equilibrium state of a system is characterised by a set of values of the thermodynamic coordinates that does not depend on the way in which the equilibrium state was reached. Processes that are, effectively, a succession of equilibrium states can also be described in terms of the thermodynamic coordinates, but this is not true for processes in which there are finite gradients in one or more of the intensive coordinates. Such processes are irreversible. However, provided that a given process takes place between two equilibrium states of the system, thermodynamics can be used to relate the values of the coordinates in these two equilibrium states, even though no information can be gained about the process itself. The technique, which has been described already, is to find a notional reversible process linking the required initial and final equilibrium states and then use that process to determine the relation between the coordinates. This approach will now be applied to two important irreversible processes: the Joule process (free expansion) in which the initial and final states of the system are true equilibrium states and the Joule—Thomson process, which is a continuous flow process.KeywordsMolar VolumeInversion TemperatureMolar Heat CapacityFixed MassFree ExpansionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.