Unit 13, Ch. 22 – Redox Reactions

Oxidation Is Losing e- Reduction Is Gaining e- Vocab - Oxidation Loss of e- Gain of oxygen Reduction Gain of e- Loss of oxygen Oxidation Is Losing e- Reduction Is Gaining e- Oxidation – reduction reaction: Any chemical change in which one compound is oxidized (loses electrons) and another compound is reduced (gains electrons); also called a redox reaction.

Mg + S → Mg2+ + S2- Oxidation : Mg → Mg2+ + 2e- (loss of electrons) Loses e-s magnesium atom is said to be oxidized to a magnesium ion Sulfur atom gains two e-s and is reduced to a sulfide ion Oxidation : Mg → Mg2+ + 2e- (loss of electrons) Reduction: S + 2e- → S2- (gain of electrons) Half- Reactions: shows either reduction or oxidation, but not both. Only the species of atom that is involved in the change Sample Prob 22-1 remember that individual atoms and compounds are neutral (have no charge) 2AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + 2Ag(s)

Practice Assigning Oxidation #s Use the oxidation numbers to identify which atoms are oxidized and which are reduced in each reaction. a. Cl2(g) + 2HBr(aq) → 2HCl(aq) + Br2(l) b. C(s) + O2(g) → CO2(g) c. Zn(s) + 2MnO2(s) + 2NH4Cl(aq) → ZnCl2(aq) + Mn2O3(s) + 2NH3(g) + H2O(l)

- The substance that is oxidized is called the reducing agent. - The substance that is reduced is called the oxidizing agent. - Single replacement and combustion reactions are redox reactions, double replacement is not a redox reaction.

Electrochemistry: The branch of chemistry that is the study of the relationship between electric forces and chemical reactions. Voltage: The potential difference or electromotive force, measured in volts; it represents the amount of work that moving an electric charge between two points would take. Electrode: A conductor used to establish electrical contact with a nonmetallic part of a circuit, such as an electrolyte. electrochemical cell: A system that contains two electrodes separated by an electrolyte phase. Cathode: The electrode on whose surface reduction takes place. Anode: The electrode on whose surface oxidation takes place; anions migrate toward the anode, and electrons leave the system from the anode.