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Rudolf Žitný, Ústav procesní a zpracovatelské techniky ČVUT FS 2010

This course is approximately at this level. CHEMISTRY E182019. CH9. Electrochemistry. Rudolf Žitný, Ústav procesní a zpracovatelské techniky ČVUT FS 2010. ELECTROCHEMISTRY. CH9. Basic concepts. Ohm's law. where R is resistance [  ], I is current and U is voltage [V]. Faraday's law.

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Rudolf Žitný, Ústav procesní a zpracovatelské techniky ČVUT FS 2010

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  1. This course is approximately at this level CHEMISTRYE182019 CH9 Electrochemistry Rudolf Žitný, Ústav procesní a zpracovatelské techniky ČVUT FS 2010

  2. ELECTROCHEMISTRY CH9 Basic concepts Ohm's law where R is resistance [], I is current and U is voltage [V]. Faraday's law where n is the amount of reacted substance [mol], I is current [A], t is time [s], z is the number of electrons in the electrode reaction and F is the Faraday constant [96487 C/mol]. Remark: 1 Coulomb is electrical charge of 6.242 × 1018electrons. 1 Ampere is electrical current of 1C/second. 1mole of reactant releases 6.02x1023z electrons, therefore 6.02x1023z/ 6.242 × 1018 =96487z Coulombs.

  3. Zn Cu Zn++ Cu++ Galvanic cell CH9 Zinc electrode submerged into an electrolyte has the tendency to be dissolved (oxidised) into cations. Free electrons are produced. Copper electrode submerged into electrolyte absorbs (reduces) cations and neutral Cu . Negative potential is necessary if K+ or Zn++ would be reduced There is a tendency to reduce cations from electrolyte. There is a tendency to push out electrons from electrode, manifested by electromotive force (potential) CATHODE ANODE Underpressure of electrons Overpressure of electrons

  4. GALVANIC Daniel CELL CH9 Cathode (Cu++ is removed from electrolyte) reduction Anode (Zn is dissolved into electrolyte) oxidation Anions Cl- compensate charge of dissolved Zn++ anions SO4-- flow through porous plug

  5. Lemmon cell CH9

  6. ELECTROCHEMISTRY CH9 The dependence of an electrode potential on the concentration of reduced and/or oxidised substances is given by the Nernst equation, which relates the potential in a non-standard state, the standard potential and the reaction quotient for the reaction . For the reduction half-reaction the Nernst equation has the form For the cell reaction the Nernst equation has the form

  7. Tutorial Daniel cell CH9 Calculate the potential at 25 C for the Daniell cell. The Cu2+ concentration is 2 mol.dm-3, the Zn2+ concentration is 0.5 mol.dm-3. cathode Ered0 =0.337 V anode Eox0 =0.763 V sum Ecell0 =1.10 V The standard cell potential is 1.1 V. The cell does not operate under standard conditions, so we have to use the Nernst equation to determine the dependence of the cell potential on the concentrations of reactants and products. Cell potential will decrease with decreasing concentration of copper ions and increasing concentration of zinc ions.

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