The influence of chemical reactions among the components of the arc atmosphere on the radial temperature distribution is discussed. Their effect on other arc plasma characteristics and the spectrochemieal determination of elements in the arc is considered. The discussion is made in terms of the E lenbaas-H eller equation for the energy balance of the plasma. The equation is solved according to Maecker. The arc model is a freely burning arc, under conditions usually applied in spectrochemical practice. The role of dissociation energy is discussed on the basis of a theoretical model. Experimental and theoretical data for the radial temperature distribution of an arc burning in nitrogen are compared to check the appropriateness of the applied procedures.