Electrochemistry

Electrochemistry

Electrochemistry is the study of the relationship between electricity and chemical reactions. For civil engineers, this is primarily important for understanding corrosion of steel structures and reinforcement.

Redox Reactions

Oxidation-Reduction (Redox) reactions involve the transfer of electrons.

Definitions

  • Oxidation: Loss of electrons (Oil RIG: Oxidation Is Loss).
    • Occurs at the Anode.
    • Example: Fe→Fe2++2e−Fe \rightarrow Fe^{2+} + 2e^-
  • Reduction: Gain of electrons (RIG: Reduction Is Gain).
    • Occurs at the Cathode.
    • Example: O2+2H2O+4e−→4OH−O_2 + 2H_2O + 4e^- \rightarrow 4OH^-

Galvanic and Electrolytic Cells

  • Galvanic (Voltaic) Cell: Spontaneous redox reaction generates electricity (e.g., Batteries).
  • Electrolytic Cell: Electrical energy drives a non-spontaneous reaction (e.g., Electroplating).

Standard Reduction Potentials (E∘E^\circ)

The tendency of a species to gain electrons is measured relative to the Standard Hydrogen Electrode (SHE, 0.00 V).

Ecell∘=Ecathode∘−Eanode∘E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}

Corrosion and Prevention

Corrosion is an electrochemical process where metals deteriorate due to reactions with the environment.

Rusting of Iron

Anode (Oxidation): 2Fe(s)→2Fe2+(aq)+4e−2Fe(s) \rightarrow 2Fe^{2+}(aq) + 4e^-

Cathode (Reduction): O2(g)+2H2O(l)+4e−→4OH−(aq)O_2(g) + 2H_2O(l) + 4e^- \rightarrow 4OH^-(aq)

Overall: 2Fe+O2+2H2O→2Fe(OH)2→Fe2O3⋅xH2O (Rust)2Fe + O_2 + 2H_2O \rightarrow 2Fe(OH)_2 \rightarrow Fe_2O_3 \cdot xH_2O \text{ (Rust)}

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