For reactions which are incomplete, the equilibrium constant can be determined as a function of temperature. The enthalpy of reaction is then found from the van 't Hoff equation as Δ Δ rxn H ⊖ ⊖ = R T 2 d d T ln ⁡ ⁡ K e q . A closely related technique is the use of an electroanalytical voltaic cell, which can be used to measure the Gibbs energy for certain reactions as a function of temperature, yielding K e q ( T ) and thereby Δ Δ rxn H ⊖ ⊖ .