Abstract: The invention is a method of handling the enthalpy of reaction of fast homogeneous gas-phase chemical reactions, by using mechanical energy in the form of work performed by moving surfaces in contact with the reactants, for adding energy to or removing energy from the gaseous reactants. Transfer of energy is obtained by adiabatic compression or expansion of the gas, or by adiabatic dissipation of mechanical energy into heat. The invention further relates to an apparatus for carrying out fast homogeneous gas phase chemical reactions wherein the said principles are applied in the reactor and to a process for cracking hydrocarbons wherein the said principle is applied in the reactor.