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Electrochemical Cells

Electrochemical cells are the cells in which chemical energy is transformed into electrical energy. This means that chemical reactions produce electric current.

Cell notation of an electrochemical cell

  • Anode is written on the left side, and cathode is written on the right side.
  • Phase boundaries are indicated by vertical bar or slash.
  • Concentration of the electrolytes in the anode and cathode must be written in parenthesis.
  • In case of a gas, the partial pressure is to be mentioned in atm or mm Hg.
  • A comma is used to separate two chemical species present in the same solution.
  • A double vertical line, i.e., | |, denotes that a salt bridge is present.
EMF of the cell is written on the extreme right of the representation. For example:
  1. Zn(s) | ZnSO4(c1 M) || CuSO4(c2 M) | Cu(s); Ecell
  2. Pt | H2(P1atm) | HCl (c M) | AgCl(s) | Ag; E cell
  3. Pt | Fe2+ (c1 M), Fe3+(c2 M) || Ag+ (c M) | Mg; E°cell

Cell potential and Nernst equation

Nernst equation is used to relate either half-cell potential or EMF of a cell with the concentration of the involved species. Let us first consider a redox change occurring in an electrochemical cell.
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– ΔG = nF × Ecell; –ΔG° = nFE°cell
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Relation between standard free energy and equilibrium constant is given by
ΔG° = –2.303 RT log Keq

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