Van 't Hoff equation


The Van 't Hoff equation in chemical thermodynamics relates the change in the equilibrium constant, Keq, of a chemical equilibrium to the change in temperature, T, given the standard enthalpy change, ΔHo, for the process. The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy from the formation of 1 mole of the compound from its constituent elements, with all substances in their standard states at 1 atmosphere (1 atm or 101.3 kPa). The equation is often integrated between two temperatures under the assumption that the reaction enthalpy ΔH is constant. The definite integral between temperatures T1 and T2 is depended on the equilibrium constants at the absolute temperatures T1 and T2. (The equilibrium constant of a chemical reaction is the value of the reaction quotient when the reaction has reached equilibrium. At any given temperature, the equilibrium constant has a value which is independent of the initial and actual concentrations of the reactant and product species.)

Related formulas


K1The equilibrium constant at absolute temperature T1 (dimensionless)
K2The equilibrium constant at absolute temperature T2 (dimensionless)
ΔHThe standard enthalpy change (J/mol)
Rmolar gas constant
T2Absolute temperature (K)
T1Absolute temperature (K)