11Chapter 17ElectrochemistryRedox ReactionsElectrochemistry is the study of batteries and interconversion of chemical and electrical energy. Based on redox (oxidation-reduction) reactions in which one element gains electrons and another loses electrons.These two processes MUST happen together.Have to assign oxidation numbers to determine (see Chapter 4).Oxidation NumbersElements in their natural states are 0.Elements in binary ionic compounds are the same as their charges.H: usually +1 except with alkali metals it’s aH: usually +1, except with alkali metals it s a -1(LiH, NaH, etc.)O: usually -2, except in peroxides it’s a -1 (H2O2, K2O2)The non-oxygen element in a polyatomic ion has to be determined from the other oxidation numbers.
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22Redox ReactionsOxidation: loss of electronsReduction: gain of electronsLEO the lion goes GER or OIL RIGThe substance oxidized is also called the reducing agent (it caused the other substance to be reduced). And vice versa.Cu(s) + AgNO3ÆAg(s) + Cu(NO3)2Cu(s) + AgNO3(aq)Redox ReactionsCH4(g) + O2(g) ÆCO2(g) + H2O(g)Na(s) + HCl(aq) ÆNaCl(aq) + H2(g)For each reaction:What is oxidized, reduced?What is the oxidizing agent? Reducing agent?Combustion, decomposition, combustion, and single-replacement reactions are all redox.