The equilibrium relationships among various nitrogen species are summarized in Table 16.2 The equilibrium constants given here were calculated from the values documented in the Appendix. Recently Van Cleemput and Baert (1974) summarized their own compilation of free energy values for biological environments. Nitrogen equilibria can be combined in many different ways to show the equilibrium relationships among the various nitrogen species. Many such equilibria will be demonstrated in the sections that follow.