Reduction and oxidation represent one type of processes around us. Reduction-oxidation reactions can be described by a chemical equation. The law of mass conservation dictates that the number of atoms of an element on the left hand side of the equation equals the number of atoms of this element on the right hand side. The stoichiometric numbers of a balanced equation need to be determined. This can be done either by means of oxidation numbers of individual elements or by solving a system of linear equations.