CHEM 1001 Chapter Notes - Chapter 20: Standard Electrode Potential, Standard Hydrogen Electrode, Electrode Potential
29 Jun 2018
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CHAPTER 20: Electrochemistry
20.1 Electrode Potentials and Their Measurement
Electrode: strip of metal.
Half-cell: electrode in a solution containing ion versions of itself
Anode: where oxidation takes place… Cathode: where reduction takes
place
From salt bridge, anions migrate towards anode & cations migrate towards
cathode. And electrons travel from anode to cathode.
Salt-bridge: porous barrier or 3rd solution in U-tube
2 half cells + voltmeter + salt bridge = electrochemical cell. Cell voltage /
potential difference is driving force of e-; more V = more movement. 1 V =
1 J/C. Usually called voltaic/galvanic cell because they produce electricity
as a result of spontaneous reactions
Cell diagram: anode metal|anode ion || cathode ion|cathode metal & cell
voltage listed. The | represents boundary between different phases & ||
represents salt bridge.
20.2 Standard Electrode Potentials
Standard hydrogen electrode (SHE): 2H+ + 2e- H2(g) done on inert Pt
electrode and Eºcell = 0V. Comparing others’ voltage to this decides if they
are better oxidizing agents.
Standard electrode potential (Eº): measures tendency for reduction
process to occur. Eºcell = Eº(right/cathode) - Eº(left/anode) and remember…
the anode one is reversed from given E value in table (since reverse reaction)
20.3 Ecell, ΔG, and K
ΔG = -zFEcell where F is Faraday constant (96485 C/mol of e-) and z = # of
e- transferred between electrodes. Note: ΔG = -w
If ΔG is positive, Ecell must be negative, and vice versa. Note: Ecell is
intensive property, so doesn’t change if coefficients change… stays same.
Eºcell = (RT/zF) lnK
20.4 Ecell as a Function of Concentrations
Nerst equation: Note: ln = 2.303log…
If finding whether reaction is spontaneous or not, find Ecell, not Eºcell
Can find Ksp using this equation too where anode & cathode contain same
element but in different concentrations. Eºcell = 0, Ecell is given, & solve
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Document Summary
Half-cell: electrode in a solution containing ion versions of itself. Anode: where oxidation takes place cathode: where reduction takes place. From salt bridge, anions migrate towards anode & cations migrate towards cathode. Salt-bridge: porous barrier or 3rd solution in u-tube. Cell voltage / potential difference is driving force of e-; more v = more movement. Usually called voltaic/galvanic cell because they produce electricity as a result of spontaneous reactions. Cell diagram: anode metal|anode ion || cathode ion|cathode metal & cell voltage listed. The | represents boundary between different phases & || represents salt bridge. Standard hydrogen electrode (she): 2h+ + 2e- h2(g) done on inert pt electrode and e cell = 0v. Comparing others" voltage to this decides if they are better oxidizing agents. Standard electrode potential (e ): measures tendency for reduction process to occur. E cell = e (right/cathode) - e (left/anode) and remember the anode one is reversed from given e value in table (since reverse reaction)
