Normal mean stress and rates of relaxation processes are studied for strongly vibrational-chemically non-equilibrium viscous flows. For the state-to-state and multi-temperature models, the scalar forces are introduced so as to derive the corresponding fluxes in symmetric form; the reciprocity Onsager-Casimir relations are verified for each case. It is shown that due to the cross-coupling effects, the mass action law and production terms in the Landau-Teller form cannot be used in viscous non-equilibrium flows.