Van't Hoff Equation
The equation describing how an equilibrium constant varies with temperature.
Formula / equation
ln(K₂/K₁) = −ΔH°/R (1/T₂ − 1/T₁)
Unit
kJ/mol
In depth
Plotting ln K against 1/T gives a straight line whose gradient is −ΔH°/R, making it a standard way to determine reaction enthalpy without calorimetry. The equation quantifies Le Chatelier's temperature rule: K rises with temperature only for endothermic reactions.
Examples in the real world
Measuring K for ester hydrolysis at several temperatures and extracting ΔH° from the van't Hoff plot.