The reactants appear to the left of the arrows, in this example they are H 2 {\displaystyle {\ce {H2}}} (hydrogen), O 2 {\displaystyle {\ce {O2}}} (oxygen) and C (carbon). The products appear to the right of the arrows, here they are H 2 O {\displaystyle {\ce {H2O}}} (water) and CO 2 {\displaystyle {\ce {CO2}}} (carbon dioxide). In this example, since the reactions are irreversible and neither of the products are used up in the reactions, the set of reactants and the set of products are disjoint.