Resources | Subject Notes | Chemistry
Redox reactions, short for reduction-oxidation reactions, are chemical reactions that involve the transfer of electrons between two species. These reactions always occur together; one species is oxidized (loses electrons) while the other is reduced (gains electrons). Understanding redox reactions is fundamental to chemistry.
Oxidation is the loss of electrons by a substance. It's often, but not always, associated with the gain of oxygen. A helpful mnemonic is OIL RIG: Oxidation Is **L**oss (of electrons).
In a redox reaction, the substance that undergoes oxidation is called the reducing agent because it causes the other substance to be reduced.
Reduction is the gain of electrons by a substance. A helpful mnemonic is OIL RIG: Oxidation Is **L**oss (of electrons).
In a redox reaction, the substance that undergoes reduction is called the oxidizing agent because it causes the other substance to be oxidized.
| Term | Definition |
|---|---|
| Oxidation | Loss of electrons |
| Reduction | Gain of electrons |
| Reducing Agent | Substance that is oxidized and causes another substance to be reduced |
| Oxidizing Agent | Substance that is reduced and causes another substance to be oxidized |
The reaction of iron with oxygen to form iron oxide (rust):
$$4Fe(s) + 3O_2(g) \rightarrow 2Fe_2O_3(s)$$In this reaction, iron (Fe) is oxidized (loses electrons) and oxygen (O2) is reduced (gains electrons).
The reaction of hydrogen with chlorine to form hydrogen chloride:
$$H_2(g) + Cl_2(g) \rightarrow 2HCl(g)$$In this reaction, hydrogen (H2) is oxidized (loses electrons) and chlorine (Cl2) is reduced (gains electrons).
While oxidation often involves the gain of oxygen, it's crucial to remember that oxidation is defined as the loss of electrons. Reduction is defined as the gain of electrons, regardless of whether oxygen is involved.