• Changes in?temperature?and?concentration?of aqueous ions will affect the standard electrode potential (E^?) of a half-cell
• Under these?non-standard conditions,?E?is used as a symbol for the electrode potential instead of?E^?

Increasing the concentration of the species on the left

• If the concentration of the species on the left is increased, the position of equilibrium will shift to the?right
• This means that the species on the left gets?more?easily?reduced
• The?E?value becomes?more positive?(or less negative)
• Let’s look at the half-cell below as an example

Zn²⁺?(aq) + 2e^-?? Zn (s)? ? ? ??E^??= -0.76 V

• If the concentration of Zn²⁺?(species on the left) is?increased, the equilibrium position will shift to the?right
• The species on the?left?(Zn²⁺) will get more easily?reduced
• Therefore, the?E?value becomes?less negative?and will change too, for example, -0.50 V instead
• This principle can also be applied to a half-cell with a positive?E^??value such as:

Fe³⁺?(aq) + e^-?? Fe²⁺?(aq)? ? ? ??E^??= +0.77 V

• If the concentration of Fe³⁺?(species on the left) is?increased, the equilibrium position will shift to the?right
• The species on the?left?(Fe³⁺) will get more easily?reduced
• Therefore, the?E?value becomes?more positive?and will change too, for example, +0.89 V instead

Increasing the concentration of species on the right

• If the concentration of the species on the right is increased, the position of equilibrium will shift to the?left
• This means that the species on the left gets?less?easily?reduced
• The?E?value becomes?less positive?(or more negative)
• Let’s look again at the half-cell below

Zn²⁺?(aq) + 2e^-?? Zn (s)? ? ? ??E^??= -0.76 V

• If the concentration of Zn (species on the right) is?increased, the equilibrium position will shift to the?left
• The species on the?left?(Zn²⁺) will get less easily?reduced
• Therefore, the?E?value becomes?more negative?and will change too, for example, -0.82 V instead
• This principle can, again, also be applied to a half-cell with a positive?E^??value:

Fe³⁺?(aq) + e^-?? Fe²⁺?(aq)? ? ? ??E^??= +0.77 V

• If the concentration of Fe²⁺?(species on the right) is?increased, the equilibrium position will shift to the?left
• The species on the?left?(Fe³⁺) will get less easily?reduced
• Therefore, the?E?value becomes?less positive?and will change too, for example, +0.56 V instead

Effect of concentration on the electrode potential