1.6.2

Electrochemical Series

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The Electrochemical Series

Standard reduction potentials are listed in the electrochemical series.

The electrochemical series

The electrochemical series

  • We list lots of half-equations with their standard reduction potentials in a table called the electrochemical series.
    • The most negative potentials (the hardest reductions to do) are at the top.
    • The standard hydrogen electrode potential is in the middle at 0 V.
    • The easiest reductions are at the bottom.
Calculating cell potentials

Calculating cell potentials

  • We can use standard reduction potentials to calculate the standard cell potential. This will allow us to predict the outcome of reactions.
  • The process for calculating the standard cell potential is:
    • Pick your two half equations.
    • Decide which is happening as an oxidation and which is happening as a reduction.
    • Subtract the standard reduction potential for the oxidation from the potential for the reduction.
      • Eθcell = Eθreduced − Eθoxidised
E.g. Magnesium and bromine

E.g. Magnesium and bromine

  • The standard reduction potential for Mg2+ + 2e- ⇌ Mg(s) is Eθ = −2.37 V.
  • The standard reduction potential for Br2 + 2e- ⇌ 2Br-(aq) is Eθ = 1.07 V.
    • The magnesium potential is more negative, so will go in the oxidation direction.
    • The bromine potential is more positive, so the bromine will be reduced.
E.g. Magnesium and bromine cont.

E.g. Magnesium and bromine cont.

  • The equation for the reaction between magnesium and bromine is:
    • Mg(s) + Br2(aq) → MgBr2(s)
      • Eθcell = 1.07 V − (−2.37 V) = 3.44 V

Drawing Cells and Predicting Reactions

There is a standard shorthand way of drawing electrochemical cells in chemistry.

Shorthand way of drawing cells

Shorthand way of drawing cells

  • There’s a standard shorthand way of writing electrochemical cells.
    • The more negative potential goes on the left.
    • The more positive potential goes on the right.
    • The oxidised forms go in the centre.
    • The different couples are split by a double vertical line that indicates a salt bridge.
Predicting cell reactions

Predicting cell reactions

  • We can use standard cell potentials to predict whether or not a reaction is feasible.
    • If the standard cell potential is positive, the reaction is feasible.
    • If the standard cell potential is negative, the reaction is NOT feasible.
Jump to other topics
1

Physical Chemistry

1.1

Atoms, Molecules & Stoichiometry

1.2

Atomic Structure

1.3

Chemical Bonding

1.4

States of Matter

1.5

Chemical Energetics

1.6

Electrochemistry

1.7

Equilibria

1.8

Partition Coefficient

1.9

Reaction Kinetics

2

Inorganic Chemistry

3

Organic Chemistry & Analysis

3.1

Introduction to Organic Chemistry

3.2

Hydrocarbons

3.3

Halogen Derivatives

3.4

Hydroxy Compounds

3.5

Carbonyl Compounds

3.6

Carboxylic Acids & Derivatives

3.7

Nitrogen Compounds

3.8

Polymerisation

3.9

Analytical Techniques

3.10

Organic Synthesis

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