Cell potential or electromotive force: the “pull” or driving force on the electrons

○ Substance being oxidized “pushes” the electrons

○ Substance being reduced “pulls” the electrons thru the wire

• Ecell is measured in Volts (V) using a voltmeter: measures the voltage (electricity) → how much electricity is flowing thru the wire
• The total cell potential is the sum of the potential at each electrode
• Ex:

○ “Ecell = Oxidation – Reduction”

○ One of the reactions must be reversed, so the sign must be changed

• How to know which half-reaction should be reversed: For a galvanic (voltaic) cell, the overall cell potential will be POSITIVE → flip the sign of the reaction that leads to a + E° when both are summed

○ Key word = voltaic → E° must be (+)

○ Whichever half-reaction that flipped/reversed = anode

Standard Hydrogen Electrode

• E° = 0
• When changing the amount of electrons by multiplying an integer, DO NOT change/multiply E°
• Substance with most favorable reduction potential (stronger reducing power/agent) = more negative E° red
• Substance with the most favorable oxidation potential (stronger oxidizing power/agent) = more positive E° red

Description of a Galvanic Cell

3 things for a complete description:

1. Cell potential (+) and balanced cell reaction
2. Direction of electron flow
3. Designation of anode and cathode

Favorability of a Galvanic Cell

• The reaction always run spontaneously in the direction that produces a positive (total) cell potential
• If E° < 0, then ΔG° > 0 → nonspontaneous
• If E° > 0, then ΔG° < 0 → spontaneous

Free Energy and Cell Potential

• ΔG° = –nFE° (on RFS)

○ N = number of moles = coefficient of the number of electrons that you canceled out

○ F = Faraday’s constant = 96,485 (J/vmol)