A historical overview about the development of thermodynamic calculations and their application to stellar atmospheres is given. Thermochemical equilibrium chemistry for major and trace elements in carbon star atmospheres is discussed. The calculations indicate TiC, graphite and SiC dust formation within 1–3 stellar radii from the photosphere. Trace element abundance patterns observed in circumstellar SiC grains isolated from meteorites are modeled by fractional condensation. The complementary trace element patterns in SiC grains and those in N-star atmospheres are plausibly explained by fractional condensation during stellar variability cycles.