How do you identify oxidation and reduction in half equations?

In half equations, oxidation is identified by a gain of oxygen or loss of hydrogen, while reduction is a loss of oxygen or gain of hydrogen.

In more detail, oxidation and reduction are two key concepts in the field of redox (reduction-oxidation) reactions. These reactions involve the transfer of electrons between chemical species. Oxidation is the process where a substance loses electrons, and this can be represented in a half equation by an increase in oxidation state. This often occurs through the gain of oxygen or the loss of hydrogen. For example, in the half equation 2H2 -> 4H+ + 4e-, hydrogen is being oxidised as it is losing electrons.

On the other hand, reduction is the process where a substance gains electrons, which can be represented in a half equation by a decrease in oxidation state. This often happens through the loss of oxygen or the gain of hydrogen. For example, in the half equation O2 + 4e- -> 2O2-, oxygen is being reduced as it is gaining electrons.

It's important to remember that in a redox reaction, one species is always oxidised and another is always reduced. This is often summarised by the phrase 'OIL RIG', which stands for 'Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons)'. By identifying the changes in oxidation state in half equations, you can determine which species are being oxidised and which are being reduced.