Chapter IX. Laws of Kinetics of Nonisothermal Chain Processes

Abstract

The rarely considered fundamental difference between the temperature dependences of the reaction rate and the rate constant is emphasized. The small change in the rate of reactions with high activation energies, contrary to existing ideas, is illustrated. It was shown that the main reason for the deviation between the calculated and experimental rates is the neglect of the temperature dependence of the reagent concentrations during the reaction. It has been shown that the main reason for the deviation between the calculated and experimental rate values is the neglect of the temperature dependence of the reactant concentrations in the course the reaction. The concept of the temperature rate constant is introduced: the change in the rate with a unit change in temperature, i.e., the temperature derivative of the rate constant. It is shown that this characteristic determines the competition between the stages of a complex process under nonisothermal conditions. The law of temperature dependence of the chain process was discovered, and its agreement with experiment was verified. The difference between the self-acceleration of a reaction from an increase in temperature and from the multiplication of active particles is explained. An experimental illustration is provided. The difference between the temperature dependences of the reaction rates in a gas heated from outside before and after the onset of ignition is explained. Based on experimental data, the determining role of the hydrogen atom concentrations in the combustion rate at hundredths of atmospheric pressure and at atmospheric pressure is quantitatively demonstrated. This demonstrates the determining role in combustion of the conversion of a significant part of the enthalpy of the initial reagents into the free-valence energy.