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19 - Electrochemistry and Its Applications

19 - Electrochemistry and Its Applications - Chapter 19...

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Chapter 19: Electrochemistry and Its Applications Redox reactions involve the transfer of electrons from one atom, molecule, or ion to another Electrochemistry is study of relationship between electron flow and redox reactions; relationship between electricity and chemical changes Voltage produced by an electrochemical reaction depends on oxidizing and reducing agents used as reactants 19.1Redox Reactions Redox reactions involve o Presence of strong oxidizing or reducing agents as reactants o Change in oxidation number o Presence of an uncombined element as a reactant or product; free elements always result in oxidation number Oxidation: loss of electrons and increase in oxidation number Reduction: gain of electrons and decrease in oxidation number Oxidizing agent is reduced and reducing agent is oxidized always reactants, never products 19.2Using Half-Reactions to Understand Redox Reactions Half-reactions make up a redox reaction; one half-reaction for the oxidation and one half-reaction for the reduction; shows the transfer of electrons Net reactions – electrons are conserved Balancing Redox Equations Using Half-Reactions o Balancing Redox Equations in Acidic Solutions Recognize whether the reaction is an oxidation-reduction process. If it is, then determine what is reduced and what is oxidized. Break the overall unbalanced equation into half-reactions. Balance the atoms in each half-reaction. Balance all atoms except for O and H, then balance O by adding H 2 O and balance H by adding H + (acidic solution so OH - cannot be used since OH - concentration is very low) Balance half reactions for charge using electrons Multiply the half-reactions by appropriate factors so that the oxidation half-reaction produces as many electrons as the reduction half-reaction accepts Add half-reactions to give overall reaction and cancel equal amounts of reactants and products that appear on both sides of the arrow Check the balanced equation to make sure both atoms and charge are balanced Add enough water molecules to both sides of equation to convert all H + to H 3 O + Check final results to make sure both atoms and charges are balanced o Balancing Redox Equations in Basic Solutions Final electrochemical reaction only has water and OH -

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