Half equations are most often used in redox reactionA redox reaction is one in which oxidation and reduction occur at the same time. and in electrolysisIs the decomposition of a liquid electrolyte using a direct current of electricity.. They involve either atoms and molecule gaining or losing electrons to become ions, or ions gaining or losing electrons to become atoms and molecules.
Either way, the process for writing the equation is the same.
Write down the reactant and the product.
Balance the atoms.
Write the total charge underneath each species in the equation.
Balance the charge by adding electrons.
For example, you may be asked to write the half equation for the conversion of oxide ions into an oxygen molecule.
Step
Action
Half equation
1
Write down the reactant and the product.
O2- 鈫 O2
2
Balance the atoms.
2O2- 鈫 O2
3
Write the total charge underneath each species in the equation.
袄(袄蹿谤补肠调调20皑镑调2-皑皑调(-4)皑鈫抃蹿谤补肠调调0皑冲2皑调(0)皑袄)
4
Balance the charge by adding electrons.
2O2- 鈫 O2 + 4e-
Step
1
Action
Write down the reactant and the product.
Half equation
O2- 鈫 O2
Step
2
Action
Balance the atoms.
Half equation
2O2- 鈫 O2
Step
3
Action
Write the total charge underneath each species in the equation.