The vapour-liquid-equilibrium (VLE) of pure fluids and mixtures is important to the study of CO2 capture. CO2 capture aims to assist in the reduction of atmospheric CO2 levels. A main CO2 capture method is reactive absorption of an aqueous solvent in equilibrium with its vapour. In our first study, we develop a new algorithm for the prediction of VLE and apply it to macroscopic thermodynamic models and molecular simulation data for non-electrolytes. In the second study, we develop a new thermodynamic framework for the molecular simulation of VLE that involves reactions in the vapour phase. We apply this analysis to recently published data for molten NaCl. This methodology can be easily extended to the analysis of molecular simulation data for ionic liquids (ILs) which has become increasingly important in the study of CO2 capture.