Non-equilibrium boundary conditions based upon kinetic theory and linear irreversible thermodynamics are applied to the interface kinetics in vapor crystal growth of unitary and binary materials. These are compared to equilibrium boundary conditions in a simple, 1D closed ampoule physical vapor transport model. It is found that in cases where the diffusive impedance is negligible and when system pressure is low, surface kinetics play an important role in limiting the mass transport. In cases where diffusion is the dominant transport impedance, and/or when the pressure in the system is high, the kinetic impedances at the interfaces are negligible, as impedances due to diffusion and latent heat transport at the interfaces become more significant. The non-equilibrium boundary conditions are dependent upon the sticking coefficient of the surface. An experiment to estimate the sticking coefficient on solid surfaces is proposed. The non-equilibrium theory also predicts significant temperature jumps at the interfaces.