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A reducing agent (also called a reductant or reducer) is an element or compound that loses (or "donates") an electron to another chemical species in a redox chemical reaction. Since the reducing agent is losing electrons, it is said to have been oxidized. If any chemical is an electron donor (reducing agent), another must be an electron recipient (oxidizing agent). A reducing agent is oxidized because it loses electrons in the redox reaction. Thus reducers are "oxidized" by oxidizers and oxidizers are "reduced" by reducers; reducers are by themselves reduced (have more electrons) and oxidizers are by themselves oxidized (have fewer electrons). A reducing agent typically is in one of its lower possible oxidation states and is known as the electron donor. Examples of reducing agents include the earth metals, formic acid, and sulfite compounds. For example, consider the overall reaction for aerobic cellular respiration: :C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(l) The oxygen (O2) is being reduced, so it is the oxidizing agent. The glucose (C6H12O6) is being oxidized, so it is the reducing agent. In organic chemistry, reduction more specifically refers to the addition of hydrogen to a molecule, though the aforementioned definition still applies. For example, benzene is reduced to cyclohexane in the presence of a platinum catalyst: :C6H6 + 3 H2 → C6H12 In organic chemistry, good reducing agents are reagents that deliver H2. Historically, reduction referred to the removal of oxygen from a compound, hence the name 'reduction'. The modern sense of donating electrons is a generalisation of this idea, acknowledging that other components can play a similar chemical role to oxygen. ==Characteristics== Consider the following reaction: :2 + → 2 + 2 The reducing agent in this reaction is ferrocyanide (). It donates an electron, becoming oxidized to ferricyanide (). Simultaneously, the oxidizer chlorine is reduced to chloride. Strong reducing agents easily lose (or donate) electrons. An atom with a relatively large atomic radius tends to be a better reductant. In such species, the distance from the nucleus to the valence electrons is so long that these electrons are not strongly attracted. These elements tend to be strong reducing agents. Good reducing agents tend to consist of atoms with a low electronegativity, the ability of an atom or molecule to attract bonding electrons, and species with relatively small ionization energies serve as good reducing agents too. "The measure of a material to oxidize or lose electrons is known as its oxidation potential".〔(Electrode Reduction and Oxidation Potential )〕 The table below shows a few reduction potentials that could easily be changed to oxidation potential by simply reversing the sign. Reducing agents can be ranked by increasing strength by ranking their oxidation potentials. The reducing agent is stronger when it has a more positive oxidation potential and weaker when it has a negative oxidation potential. The following table provides the reduction potentials of the indicated reducing agent at 25 °C. To tell which is the strongest reducing agent, one can change the sign of its respective reduction potential to make it oxidation potential. The bigger the number, the stronger the reducing agent. For example, among Na, Cr, Cu and Cl−, Na is the strongest reducing agent and Cl− is the weakest one. Common reducing agents include metals potassium, calcium, barium, sodium and magnesium, and also compounds that contain the H− ion, those being NaH, LiH, LiAlH4 and CaH2. Some elements and compounds can be both reducing or oxidizing agents. Hydrogen gas is a reducing agent when it reacts with non-metals and an oxidizing agent when it reacts with metals. :2 Li(s) + H2(g) → 2 LiH(s) Hydrogen acts as an oxidizing agent because it accepts an electron donation from lithium, which causes Li to be oxidized. Half reactions: 2 Li(s)0 → 2 Li(s)+ + 2 e−::::: H20(g) + 2 e− → 2 H−(g) :H2(g) + F2(g) → 2 HF(g) Hydrogen acts as a reducing agent because it donates its electrons to fluorine, which allows fluorine to be reduced. Half reactions: H20(g) → 2 H+(g) + 2 e−::::: F20(g) + 2 e− → 2 F−(g) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「reducing agent」の詳細全文を読む スポンサード リンク
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