Two chemical models of the plasma, which describe the mixture of free electrons, ions, and atoms, are derived using identity transformations based on the equation of state of the “physical” model of the plasma, in which an interacting mixture of electrons and nuclei (protons) us considered. These chemical models satisfy Onsager’s bookkeeping rule (the equation of state is independent on the position of the bookmark, viz., the boundary separating free and bound states). The effect of excited states of an atom on the equation of state and ionization equilibrium is analyzed. It is concluded that the contribution of the Debye attraction in traditional “chemical” models is overestimated. The relations obtained for the ionization potential lowering and the equations of state differ significantly from the generally accepted expressions and explain qualitatively the experimentally observed effect of “ideality” of a nonideal plasma.