Ch17 Electrochemistry PDF

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Ch17 Electrochemistry...

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Chapter 17: Electrochemistry ● Conversion of electrical and chemical energy through oxidation-reduction reactions ● Electrons are transferred through 2 separate half-reactions ● Spontaneous chemical reactions can create electrical energy ● Electrical energy can drive reactions that are nonspontaneous 17.1 Electrochemical cells ● Half reactions are separated in space in an electrochemical cell ● Each half reaction occurs on an electrode ● Electrons at the oxidation electrode are transferred through a wire ● Electrodes are connected by an ionic conductor to maintain electrical neutrality ● Galvanic cell has spontaneous reactions that make Gibbs free energy available to do work ● Electrolytic cell can do electrical work on another system ● Control reversible chemical reactions by supplying or extracting electrical energy 17.1.1 Galvanic cells ● Salt bridge functions as Ionic conductor ● Ammeter: measures current between the electrodes ● Anode: oxidation ● Cathode: reduction ● Electrochemical cell notation ○ Oxidation reaction is always written on the left ○ | separates phase, || separates electrodes 17.1.2 Electrolytic cells ● Charged particles spontaneously seek states of lowest electrostatic potential energy ● Electrons flow from anode → cathode, high PE → low PE, negative potentials → positive potentials ● Electrolytic cells provide external driving force to make the reverse reaction spontaneous ● Electrostatic potential � is measured in volts ● Electrostatic potential energy Ep is measured in Electric volts (eV) ● Electrostatic potential has opposite sign as potential energy ● Spontaneous processes are when change in PE0 ● Voltmeter measures potential differences between two half-cells ○ Gives the cell potential, or voltage 17.1.3 Faraday’s Laws 1. The mass of a given substance that is produced/consumed in an electrochemical reaction is proportional to the quantity of electric charge passed. 2. Equivalent masses of different substances are produced or consumed in electrochemical reactions by a given quantity of electric charge passed. ● Faraday constant: electrical charge per mole of electrons ● Electric current: charge that flows through a circuit per second ○ Measured in amperes ○ Coulombs = amps x seconds 17.2 Cell Potentials and the Gibbs Free Energy ● Electrical work done on electrons: change in PE of the electrons

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In a galvanic cell running spontaneously ○ � G...