The energy balance equation and the component balance equations for continuous systems in a stationary state are used to derive a certain function of temperature, which includes the heat conductivity of the system, the partial pressures of the components, the diffusion coefficient and thermal diffusion ratio for binary ideal gas mixtures, and the rates and heats of the chemical reactions in the system. This function is shown to satisfy the Laplace equation, from the solution of which the temperature distribution in the system can be derived. From this the following are calculated as functions of position: the diffusion and thermal diffusion fluxes and velocities, the rates of formation of the components, and the heat transported by conduction and by the chemical reactions. As an example, calculations are made for a long cylindrical tungsten halogen lamp under certain conditions of operation, including the absence of convection. It is shown that the chemical reactions make an appreciable contribution to the heat transport, even though the concentrations of the reacting components are small.