Concise Electrochemistry Notes

Electrochemical Potential

  • Electrochemistry studies the relationship between electricity and chemical reactions.
  • It's an interdisciplinary science applicable in engineering, chemistry, biology, and physics.

Electrochemical Cells

  • Systems that incorporate a redox reaction to produce or utilize electrical energy.
  • Two types:
    • Voltaic/Galvanic Cell: Releases free energy from a spontaneous reaction to produce electricity (W’ = ∆G).
    • Electrolytic Cell: Absorbs free energy from a source of electricity to drive a nonspontaneous reaction.

Voltaic/Galvanic Cell Construction

  • Based on the spontaneity of a redox reaction where \Delta G < 0.
  • Requires electrodes (anode and cathode), electrolytes (ionic salts), and half-cell separators (membranes, salt bridges).

Cell Potential (E_{cell})

  • The difference in electrical potential between the two electrodes.
  • Standard cell potential (E^o_{cell}) is measured at specified conditions (298 K, 1 atm, 1 M).

Batteries

  • Primary: Lithium ion batteries – types, working principles and advantages
  • Secondary batteries

Standard Electrode Potential

  • Measured using a reference half-cell, typically the Standard Hydrogen Electrode (SHE).
  • SHE: E^o = 0 \text{ V}
  • By convention, always refers to the half-reaction written as a reduction.

Calculation of Standard Cell Potential from Standard Half-Cell Potentials

  • E^o{cell} = E^o{\text{red. half-cell}} – E^o_{\text{ox. half-cell}}
    • Example: E{zinc} = -0.76 V and E{copper} = 0.34 V resulting in E_{ocell} = 1.1 V
  • Half-cell with a smaller or more negative E^o acts as the anode; the half-cell with a larger or more positive E^o acts as the cathode.

Electrochemical Series

  • Lists elements and molecules based on their ability to oxidize or reduce.
  • Used to predict whether a metal will react with a solution of another metal's ions.

Non-Standard State Cell Potential

  • Nernst Equation: Used to calculate E_{cell} under non-standard conditions.
  • \Delta G= \Delta G^o + RT \ln Q
  • \Delta G= -nFE{cell} \text{ and } \Delta G^o = - nFE^o{cell}
  • Relates Gibbs energy to reaction quotient, showing how E_{cell} varies with concentration.

Concentration Cells

  • Galvanic cells with two equivalent half-cells but different ion concentrations.
  • E^o{Cell} = 0 * E{cell} depends only on the difference in concentration of ions.

Reversible vs Standard Hydrogen Electrode

  • Concentration of H^+ remains constant in SHE
  • Concentration of H^+ can change in RHE

Electrolytic Cells

  • Use electrical energy to drive a nonspontaneous reaction (\Delta G > 0).
  • Involve electroplating and recovering metals from ores.
  • Faraday's Laws of Electrolysis:
    • Amount of chemical change is proportional to the quantity of electricity used.
    • Amounts of chemical changes are proportional to their equivalent weights.
  • F = 96485 \text{ C mol}^{-1}
    • F = N_A \times e = 6.023 \times 10^{23} \text{ mol}^{-1} \times 1.602 \times 10^{-19} \text{ C} = 96485 \text{ C mol}^{-1}
  • Key difference from voltaic cells: Anode is positive, and cathode is negative.