If a molecule is oxidized, does it gain or lose energy? Oxidation occurs when a molecule loses an electron or increases its oxidation state. When a molecule is oxidized, it loses energy.
In contrast, when a molecule is reduced, it gains one or more electrons. As you might have guessed, the molecule gains energy in the process.
Confused? Think about it like this. Electrons orbit the atomic nucleus, giving it electrical and kinetic energy. If you have more electrons, you have more energy. Keep in mind, however, energy input may be required (activation energy) to get a molecule to change its oxidation state.