The influence of preheating rate on kinetics of high-temperature reactions in gas - solid systems was investigated by a computer-assisted electrothermography technique. Two systems were investigated: Nb -N-2 and Ti -N-2, in the temperature ranges 2,100 - 2,500 K and 1,350-1,600 K, respectively. The results showed that for both systems reaction kinetics are enhanced by increasing the preheating rate to the desired reaction temperature.. Analysis of the experimental data in the context of the sharp-interface model showed that the activation energy of the diffusion coefficient does not depend an heating rate, while the preexponential factor is affected. Additional experiments suggest that non-isothermal preheating, even though of short duration, about 10 ms, influences chemical reactivity of the solid reactant by changing its specific surface area.