This chapter describes the canonical ensemble, which is an ensemble of systems that are all prepared in the same way with the same number of particles, volume, shape, magnetic field, and electric field. However, the energy of each system fluctuates. The chapter details experiments that involve condensed matter wherein a system is placed in contact with a heat bath that eventually reaches thermal equilibrium. It also clarifies how the system being studied together with the heat bath or combined system is thermally isolated so that its total energy is constant. The chapter illustrates a Boltzmann probability distribution, wherein probabilities are drawn along the horizontal axis and the energies along the vertical. It highlights the use of the Boltzmann probability distribution on systems that are in contact with a heat bath, granted the number of particles in the system is constant.
