A kinetic description of gas mixtures with internal degrees of freedom and chemical reactions is presented. The kinetic equations are solved using a modified Chapman-Enskog method with the transition from the governing extensive parameters to adjoint intensive ones. The advantages of this transition are discussed. It is shown that, due to this transition, a number of theorems of classical aerodynamics can be extended to nonbarotropic gas flows with physicochemical processes and the dependence of the sound velocity on intensive parameters can be found in the zero approximation of the method.