Prediction of thermodynamic properties of new compounds or mixtures is industrially important, especially when processes are established or alternatives for existing processes are evaluated. Of particular importance is the equilibrium constant, derived from the standard Gibbs energy of reaction in solution. Up to date, experimental determination is challenging, mirrored by a lack of data available. A straightforward computational way for the prediction using quantum mechanics and statistical thermodynamics is presented. The use of three standard quantum chemical methods for the determination of the ground state energies enables a comparison in terms of accuracy and computational cost. The results show that the two most laborious methods coupled cluster with single and double excitations and perturbative triple excitations and MP2 lead to comparable accuracy, whereas the fastest method density functional theory leads to considerable deviations. Hence, the method of choice for the prediction of standard Gibbs energies of reaction in solution with good accuracy at medium computational cost is MP2 combined with conductor-like screening model for real solvents COSMO-RS. (C) 2008 American Institute of Chemical Engineers.