A chemical reaction of known stoichiometry can be written in general as: \[a\rm{A}\,+\,b\rm{B}\,+\,...\rightarrow\,...\,+y\rm{Y}\,+\,z\rm{Z}\] For the reaction products Y and Z the numbers \(y\) and \(z\) are known as the stoichiometric numbers, \(\nu _{\rm{Y}}\) and \(\nu _{\rm{Z}}\), for Y and Z respectively. For the reactants the stoichiometric numbers are the negatives of the numbers appearing in the equation; for example the stoichiometric number \(\nu _{\rm{A}}\) for the reactant A is \(-a\). In other words, the stoichiometric numbers are positive for products and negative for reactants.