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CHEM 1127Q (29)
Chapter 4

CHEM 1127Q Chapter 4: Pre-lecture 5: Sections 4.2-4.4

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CHEM 1127Q
Joseph De Pasquale

4.2 Oxidation-Reduction Reactions ● Oxidation - referring to oxidation-reduction (redox) reactions ● Oxidation-reduction reaction - reactions where one or more element involved undergoes a change in oxidation number ○ Oxidation = loss of electrons = increase in oxidation number ○ Reduction = gain of electrons = decrease in oxidation number ○ Reducing agent = species that is oxidized ○ Oxidizing agent = species that is reduced ● Half reaction - the process with regard to each individual reactant in a oxidation- reduction reaction ● Oxidation-reduction reaction with ionic compounds - involves transfer of electrons ● Oxidation-reduction reaction with covalent compounds - does not involve transfer of electrons ○ ● Oxidation number (oxidation state) - charge its atom would possess if the compound was ionic ● Assigning oxidation numbers to each element in a molecule or ion 1. The oxidation number of an atom in an elemental substance is zero. 2. The oxidation number of a monatomic ion is equal to the ion’s charge. 3. Oxidation numbers for common nonmetals are usually assigned as follows: a. Hydrogen: +1 when combined with non-metals, −1 when combined with metals b. Oxygen: −2 in most compounds, sometimes −1 (so-called peroxides, O22−), very rarely −12 (so-called superoxides, O2−), positive values when combined with F (values vary) c. Halogens: −1 for F always, −1 for other halogens except when combined with oxygen or other halogens (positive oxidation numbers in these cases, varying values) 4. The sum of oxidation numbers for all atoms in a molecule or polyatomic ion equals the charge on the molecule or ion. * oxidation number is written with the sign followed by number ● Subclasses of redox reactions ○ Combustion r
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