Graphical representations of reaction mechanisms

Mechanisms for complex chemical reactions can be represented by graphs having nodes of two types [4]. One corresponds to elementary reactions and the other accounts for substances. 

It must be noted that the former correspond to elementary reactions and not to steps. It means that one reversible step corresponds to two nodes. Edges connect nodes -substances and nodes reactions provided that the substances take part in the reaction. Edges will be oriented from substance A, to reaction - E/J. A if A, is the initial reactant (a, 0) and vice 

Let us consider transformation only of intermediates assuming that the gas-phase composition has been specified. In what follows we will often use this method to study catalytic reactions (surface dynamics is investigated with constant gas composition). Transformations of surface substances can be written as 

The corresponding graph is illustrated in Fig 3(a). The Langmuir-Hinshel-wood mechanism contains a step which is an interaction between intermediates (step 3) 

We will leave it to the reader (as a simple but useful exercise) to enumerate all the cycles in all the graphs depicted in Figs. 1 and 2 and also for the Prigogine autocatalytic trigger [6]  

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