The Grandcanonical Ensemble

This chapter introduces the grandcanonical ensemble as the statistics that describes an open system that exchanges particle and energy with the surrounding. We highlight that the Poisson character of the statistics of particle number is central for this ensemble, and show that like the other ensembles, this as well provides a good model of thermodynamics in the sense that it generates a conservative thermodynamic field. We illustrate this ensemble with the ideal gas, of which we calculate particle and energy fluctuations. Here we discuss as well the so called Gibbs correct counting factor.