AP Chemistry - Electrochemistry

AP Chemistry - Electrochemistry - AP Chemistry...

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AP Chemistry - Electrochemistry Section 20.1 In an oxidation-reduction reaction electron transfer occurs between a reducing agent and an oxidizing agent. In any electron transfer reaction: One reactant is oxidized and one is reduced. The extent of oxidation and reduction must balance. The oxidizing agent (the chemical species causing oxidation) is reduced. The reducing agent (the chemical species causing reduction) is oxidized. Oxidation numbers can be used to determine whether a substance is oxidized or reduced. An element is oxidized if its oxidation number increases. The oxidation number decreases in reduction. All equations for oxidation-reduction reactions must be balanced for both mass and charge. The same number of atoms appear in the products and reactants of an equation, and the sum of electric charges of all the species on each side of the equation arrow must be the same. Charge balance guarantees that the number of electrons produced in oxidation equals the number of electrons consumed in reduction. The half-reaction method is a procedure that involves writing separate, balanced equations for the oxidation and reduction processes called half-reactions . The equation for the overall reaction is the sum of the two half-reactions, after adjustments have been made (if necessary) in one or both half-reaction equations so that the numbers of electrons transferred from reducing agent to oxidizing agent balance. When balancing equations for redox reactions in aqueous solution, it is sometimes necessary to add water molecules (H 2 O) and either H + (aq) in acidic solution or OH - (aq) in basic solution to the equation. Section 20.2
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AP Chemistry - Electrochemistry Devices that use chemical reactions to produce an electric current are called voltaic cells or galvanic cells. All voltaic cells use product-favored redox reactions composed of an oxidation and a reduction. The cell is constructed so that electrons produced by the reducing agent are transferred through an electric circuit to the oxidizing agent. Chemical energy is converted to electrical energy in a voltaic cell. The opposite process, the use of electric energy to effect a chemical change, occurs in electrolysis . Electrochemistry is the field of chemistry that considers chemical reactions that produce or are caused by electrical energy. A salt bridge allows cations and anions to move between the two half-cells connected by the bridge. The electrolyte chosen for the salt bridge should contain ions that will not react with chemical reagents in both half-cells. In all electrochemical cells the anode is the electrode at which oxidation occurs. The electrode at which reduction occurs is always the cathode . A minus sign can be assigned to the anode in a voltaic cell, and the cathode is marked
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AP Chemistry - Electrochemistry - AP Chemistry...

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