Molecular simulation is applied in combination with experimental investigations to obtainthermodynamic properties. Two newly constructed experimental apparatuses for the measurement of the vapor-liquid equilibrium (VLE) behavior of mixtures are presented. Next, abrief introduction into molecular simulation, as well as into the Peng Robinson equation ofstate (EOS) is given. Furthermore, the integration of the radial distribution function into thesimulation tool ms2 is discussed. For the mixtures nitrogen + acetone and oxygen + acetone, a set of new VLE data are generated by molecular simulation and experiment. For further applications, the Peng-RobinsonEOS is adjusted to the obtained data. In addition, new force field models are developed for the siloxanes hexamethyldisiloxaneand octamethylcyclotetrasiloxane, for decafluorobutane, for hydrazine and for its derivativesmonomethylhydrazine as well as 1,1-dimethylhydrazine and validated with experimentaldata from the literature. Unlike dispersive interactions are adjusted to experimental datafrom the literature for various mixtures containing the hydrazines. Furthermore, the PengRobinson EOS is adjusted for these mixtures. Additionally, the Henrys law constant forthe solubility of different gases in liquid hydrazine, monomethylhydrazine and dimethylhydrazine is computed. The mixture carbon dioxide + 2,2-dimethyl-1-propanol is studied by experiment. New VLEdata for this mixture are reported for the two isotherms 333 and 353 K. The Peng-RobinsonEOS is adjusted to these data points as well.