Two physical properties of ionic liquids were studied for this thesis, namely diffusion coefficients and octanol-water partition coefficients (KOW). Diffusion coefficients of CO2 into various ionic liquids (IL) were measured at atmospheric pressure because they are needed for properly designing processes. Values of the diffusion coefficients ranged between 1.8 x 10-6 cm2/s for an IL with viscosity of 603 cP and 1.2 x 10-5 cm2/s for an IL with viscosity of 14 cP. Diffusion coefficients increased in a linear fashion with the inverse of the IL's viscosity. KOWs of imidazolium-based ILs were measured to help characterize ILs' potential environmental impact prior to widespread industrial use. The effect of chemical structure on the KOW was measured. The KOWs were extremely low, ranging between 0.001 and 11.1, indicating that the ILs have extremely low bioconcentration and soil adsorption potential.