Activation energies of opposite elementary reactions and reaction enthalpy

Activation energies of opposite elementary reactions and reaction enthalpy 

From the diagram, we can deduce that the difference between the activation energies of the direct reaction and the reverse reaction is equal to the enthalpy of the reaction  

After decomposition into elementary steps reaction, it is necessary to rmderstand how this elementary step occurs. We will examine this issue in the case of a gas 

The relationship between the molecularity of a reaction and the number of molecules that must collide simultaneously during the elementary act is the basic idea of the modeling of elementary steps. Bimolecular reactions are by far the most freqnent. Sometimes the collision happens between identical species A i and A2, that is to say two molecnles of the same componnd. Tiimolecnlar reactions are extremely rare because they involve the simnltaneons colhsion of three molecules, which is an exceptional phenomenon in a gaseons or hqnid mixture with or without sohd particles. Reactions of an order eqnal or greater than fonr are excluded because the probability of four or more molecules colhding in a single impact is null. 

The first model is therefore devoted to bimolecular reactions and describes the reaction as being dne to the mechanical impact between two molecules. 

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