Electrochemistry Review

Learning Outcomes

  • Describe/interpret voltaic cells using fundamental concepts.
  • Explain the Standard Hydrogen Electrode (SHE) and its relation to standard electrode potentials.
  • Calculate E° for redox reactions and determine their spontaneity.
  • Predict effects of non-standard conditions on Ecell values.
  • Understand relationships between E°, K, and ΔG°.
  • Differentiate between electrolytic and voltaic cells.
  • Predict electrolysis products from electrolytic cells.

Lithium-Ion Batteries (LIBs)

  • Significance: Nobel Prize in Chemistry 2019 awarded for the development of lithium-ion batteries, a breakthrough in recharging technology, powering devices from smartphones to electric vehicles and enabling renewable energy storage.
  • Key Contributors: John B. Goodenough, M. Stanley Whittingham, Akira Yoshino.
  • Mechanism: LIBs operate on the intercalation of Li+ ions between a graphite cathode and a metal oxide anode, providing a light and powerful energy storage solution.

Electrochemistry

  • The study of electron movements originating from redox reactions to generate or utilize electricity in chemical processes.

Redox Reactions

  • Defined as reactions where there is a transfer of electrons between species.
    • Oxidation: Loss of electrons.
    • Reduction: Gain of electrons.

Voltaic Cells

  • Also known as galvanic cells, they generate electrical current from spontaneous reactions.
  • **Components: **
    • Two half-cells (anode and cathode) connected by a salt bridge.
    • Anode: Site of oxidation (loses electrons).
    • Cathode: Site of reduction (gains electrons).
    • Salt Bridge: Maintains charge neutrality.

Cell Potential (Ecell)

  • The potential difference between electrodes measured in volts (V), directing electron flow.

Standard Hydrogen Electrode (SHE)

  • Used as a reference for measuring voltage; consists of:
    • Inert platinum electrode in 1 M HCl with H2 at 1 bar pressure.
    • Standard potential (E°) is defined as 0 V.

Standard Electrode Potential (E°)

  • Refers to the tendency for reduction at an electrode relative to the SHE.
    • Positive E° indicates a stronger capacity to gain electrons than H+.
    • Negative E° indicates a stronger tendency to lose electrons than H2.

Standard Cell Potential (E° cell)

  • Standard cell potential measures the potential difference of a cell formed from two standard electrodes.
    • E° cell > 0 indicates a spontaneous reaction.
    • Calculation example:
      E°<em>cell=E°</em>cathode−E°anodeE°<em>{cell} = E°</em>{cathode} - E°_{anode}

Relationships between E° cell, ΔG°, and K

  • Spontaneous reactions: E° cell > 0, ΔG° < 0, K > 1.
  • Non-spontaneous reactions: E° cell < 0, ΔG° > 0, K < 1.

Electrolytic Cells

  • Cells that use electricity to induce non-spontaneous reactions.
  • Electron flow is reversed from that of voltaic cells, so:
    • Electrolytic Cell Reaction Example:
      Zn2+(aq)+Cu(s)→Zn(s)+Cu2+(aq)Zn^{2+}(aq) + Cu(s) → Zn(s) + Cu^{2+}(aq)
      E°cell = -1.103 V.

Electrolysis Predictions

  • In electrolysis, various oxidation and reduction reactions must be considered, especially depending on the electrode materials and solution used.

Practice Problems

  • Examples provided for nitration reactions, overall cell reactions, and more, focusing on understanding cell diagrams and predicting spontaneous reactions based on electrode potentials.