Oxidation & Reduction
Section: 6. Chemical Reactions | Syllabus: Cambridge AS Level Physics 9702
What are Redox Reactions? Redox Reaction A chemical reaction in which oxidation and reduction occur simultaneously. The term "redox" combines both processes. Key Point In any redox reaction, oxidation and reduction always happen together - you cannot have one without the other!
Oxidation Numbers Oxidation Number (Oxidation State) A number that indicates the degree of oxidation of an element in a compound. Written using Roman numerals. Examples of Oxidation Numbers Compound Formula Oxidation State Iron(II) chloride FeCl₂ Iron = +2 Iron(III) chloride FeCl₃ Iron = +3 Copper(I) oxide Cu₂O Copper = +1 Copper(II) oxide CuO Copper = +2 Definitions in Terms of Oxygen Oxidation The gain of oxygen by a substance.
Reduction The loss of oxygen from a substance. Example 1: Reaction of Magnesium with Oxygen 2Mg + O₂ → 2MgO Magnesium is oxidized (gains oxygen) Oxygen acts as the oxidizing agent Example 2: Reduction of Copper(II) Oxide CuO + H₂ → Cu + H₂O Copper(II) oxide is reduced (loses oxygen) Hydrogen is oxidized (gains oxygen) Identifying Redox Reactions A reaction is a redox reaction if: One substance gains oxygen while another loses oxygen Both oxidation and reduction occur together There is a transfer of electrons between substances
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