Question

(a) What is meant by the term reduction? (b) On which side of a reduction half-reaction do the electrons appear? (c) What is meant by the term reductant? (d) What is meant by the term reducing agent?

Short answer

(a) Reduction is a chemical process in which a substance gains one or more electrons, causing its oxidation state to decrease. (b) In a reduction half-reaction, the electrons appear on the left side of the equation as reactants. (c) A reductant, or reducing agent, is a substance that donates electrons to another substance in a redox reaction, causing the other substance to be reduced. (d) A reducing agent, or reductant, is a substance that donates electrons to another substance in a redox reaction, causing the other substance to be reduced while itself undergoing oxidation.

Step-by-step solution

(a) Definition of Reduction)

Reduction is a chemical process in which a substance gains one or more electrons. This process is essential in redox (reduction-oxidation) reactions, where one substance undergoes reduction by gaining electrons, while another substance undergoes oxidation by losing electrons. The species that gains electrons is said to be reduced and its oxidation state decreases. In a reduction half-reaction, the species that receives the electrons is represented on the left side of the half-reaction equation, and the species after gaining the electrons is represented on the right side. For example, in the following half-reaction, the hydrogen ions gain electrons and are reduced to hydrogen gas: $$2\mathrm{H}{\phantom{A}}^{+}+2\mathrm{e}{\phantom{A}}^{-}⟶\mathrm{H}{\phantom{A}}_2$$

(b) Electrons in a Reduction Half-Reaction)

In a reduction half-reaction, the electrons (e-) appear on the left side of the equation. This is because the electrons are gained by the species undergoing reduction, which is also represented on the left side of the half-reaction. Thus, the electrons are present as reactants in a reduction half-reaction.

(c) Definition of Reductant)

A reductant, also known as a reducing agent, is a substance that donates electrons to another substance in a redox reaction, causing the other substance to be reduced. As the reductant donates electrons, it loses them and undergoes oxidation, resulting in an increase in its oxidation state. In a redox reaction, the reductant and the oxidant react together to form a balanced chemical equation, with the reductant undergoing oxidation and the oxidant undergoing reduction.

(d) Definition of Reducing Agent)

A reducing agent, also known as a reductant, is a substance that donates electrons to another substance in a redox reaction, causing the other substance to be reduced. As the reducing agent donates electrons, it loses them and undergoes oxidation, resulting in an increase in its oxidation state. In a redox reaction, the reducing agent and the oxidizing agent react together to form a balanced chemical equation, with the reducing agent undergoing oxidation and the oxidizing agent undergoing reduction.