Because atoms are neither created nor destroyed in an ordinary chemical reaction, chemical equation must have an equal number of atoms of each element on the reactant and product sides. In addition, the net electrical charges in the reactant side must be equal to the net electrical charges in the product side.

Balancing redox reactions using change in oxidation number method

In a redox reaction, the total number of electrons gained by the oxidizing agent is equal to the total number of electrons lost by the reducing agent. The change in oxidation number method for balancing redox reaction is based on this fact. This method is used to balance redox reactions that do not occur in aqueous solutions, and also reactions that do not involve ions.

Use the following steps to balance chemical equations, using the change in oxidation state method

Step 1: Write an unbalanced chemical equation.

Step 2: Assign oxidation numbers to each atom, and determine which atoms are changing their oxidation numbers.

Step 3: Determine the number of electrons lost by each atom per molecule undergoing oxidation and the number of electrons gained by each atom per molecule being reduced.

Step 4: Balance the remaining substances by counting atoms.

Step 5: Check the final equation to be sure that each atom as well as the net charges on either side is balanced.

Ion-electron method for balancing redox reactions

In the ion-electron method (also called the half-reaction method), the redox equation is separated into two half-equations - one for oxidation and one for reduction. Each of these half-reactions is balanced separately and then combined to give the balanced redox equation.

Steps for balancing redox reaction using the ion-electron method:

Step 1: Identify the element undergoing oxidation and reduction; write separate equations for oxidation and reduction half-reactions.

Step 2: Balance the element oxidized or reduced.

Step 3: Determine the change in oxidation number of the element oxidized or reduced. Add the electrons gained or lost to the side on which the redox element has the higher oxidation number.

Step 4: Balance any elements other than hydrogen and oxygen that may be present.

Step 5: Balance hydrogen by adding water molecules.

Step 6: Add the two half-reactions together and eliminate anything that appears in identical form on both sides of the equation.