Unique calling code for a chemical reaction I'm writing a script and would like to use a "Gödel numbering" to search for specific reactions.

Is there any used procedure to assign an symbol (integer, possibly) to a chemical reaction? E.g. 
$$CH_4+4O_2=CO_2+2H_2O\ \ \ \Longrightarrow \ \ \  121231412$$
I don't know about Godel numbering specifically (though this is interesting, my being a math guy at heart), but there are existing textual systems for encoding molecules (not reactions that I know of).  From these, you may be able to encode reactions.

Two examples are InChI and SMILES.  These are Wikipedia links.