An expression for the influence of temperature upon the equilibrium constant of a chemical reaction, (d ln K ⁰/dT )_P = ΔH ⁰/RT ², where K ⁰ is the equilibrium constant, ΔH ⁰ the standard heat of the reaction at the absolute temperature T, and R the gas constant.

1. Either of two thermodynamic relations that are useful in calculating the internal energy U or enthalpy H of a system; they may be written U = F - T(∂F / ∂T )_V and H = G - T(∂G / ∂T )_P , where F is the free energy, G is the Gibbs free energy, T is the absolute temperature, V is the volume, and P is the pressure.

2. Any of the similar equations for changes in thermodynamic potentials during an isothermal process.