Chemistry Notes

24.2.5 Effect of Concentration on Electrode Potential

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Electrode Potential ()

vs ⦵

Standard Electrode Potentials (⦵) are only valid under standard conditions:

  1. Temperature of
  2. Pressure of
  3. Concentration of for all aqueous ions.

If you change any of these conditions, you are now operating under non-standard conditions. Under non-standard conditions, we drop the superscript ⦵ and use the symbol instead of ⦵.

Le Chatelier’s Principle

Standard Electrode Potential as an Equilibrium

Every Standard Electrode Potential half-equation is written as a reduction equilibrium (the reactants get reduced):

To determine how concentration changes affect the electrode potential , you simply apply Le Chatelier’s Principle

Hint

  • The higher the oxidising power becomes, the more positive becomes and the lower the oxidising power becomes, the more negative becomes.
  • Oxidising power increases if forward reaction is favoured.
  • Oxidising power decreases if backward reaction is favoured.

Changing Concentration of Species on the Left

Increasing Concentration of Species on Left

  • According to LCP, the equilibrium shifts to the right to minimise the effect of the change.
  • This favours the forward reaction (reduction).
  • The species becomes more easily reduced (higher oxidising power).

Result: The electrode potential () becomes more positive.

Decreasing Concentration of Species on Left

  • According to LCP, the equilibrium shifts to the left to minimise the effect of the change.
  • this favours the backward reaction (oxidation).
  • The species becomes harder to reduce (lower oxidising power).

Result: The electrode potential () becomes more negative.

Changing Concentration of Species on the Right

Increasing Concentration of Species on Right

  • According to LCP, the equilibrium shifts to the left to minimise the effect of the change.
  • this favours the backward reaction (oxidation).
  • The species becomes harder to reduce (lower oxidising power).

Result: The electrode potential () becomes more negative.

Decreasing Concentration of Species on Right

  • According to LCP, the equilibrium shifts to the right to minimise the effect of the change.
  • This favours the forward reaction (reduction).
  • The species becomes more easily reduced (higher oxidising power).

Result: The electrode potential () becomes more positive.

Graph View