R3.2.12, R3.2.13, R3.2.14 Standard electrode potentials & Cell potential

Standard electrode potential

Electrode potential of a half-cell measured under standard conditions relative to the SHE

SHE - Standard hydrogen electrode, assigned value of 0.00V

Standard hydrogen electrode conditions

Hydrogen pressure of 100 KPa

Solution of hydronium ions with a concentration of 1M

Inert platinum electrode

Temperature of 298K

Hydrogen either reduced to form hydrogen gas, or oxidized to form hydrogen ions

How SHE is used

SHE connected to half-cells to measure electrode potential

Reading of voltmeter tells us direction of electron flow

Positive voltage means electrons are flowing from half-cell to SHE

Sign of standard electrode potential

Positive means half-cell will undergo reduction when connected to SHE (will be cathode)

Negative means half-cell will undergo oxidation when connected to SHE (will be anode)

Table of standard electrode potential trends

More positive means reduction half-reaction occurs more readily

More negative means reduction half-reaction occurs less readily

More positive elements are better oxidizing agents

More negative elements are better reducing agents

Which half-cell will be the anode and cathode?

Half-cell with more negative standard electrode potential is anode

Half-cell with more positive standard electrode potential is cathode

Calculating cell potential

Subtract standard electrode potential of half-cell undergoing oxidation from one undergoing reduction

Subtract standard electrode potential of anode from cathode

Relationship between cell potential and spontaneity

Positive cell potential means ΔG is negative (spontaneous)

Negative cell potential means ΔG is positive (non-spontaneous)

Zero cell potential means reaction is at equilibrium

Equation for calculating Gibbs free energy from electrode potentials

Units of Gibbs free energy are J/mol