Reactivity 3.2.13 — Standard Cell Potential, \( E^\circ_{\text{cell}} \)

 The standard cell potential, \( E^\circ_{\text{cell}} \), is the electromotive force (voltage) produced by a redox reaction occurring in an electrochemical (galvanic) cell under standard conditions:

• Solutions with 1 mol dm⁻³ concentration
• Temperature of 298 K (25 °C)
• 1 atm pressure for any gases involved
• Electrodes are connected via an external circuit and a salt bridge completes the internal circuit

Formula for Calculation:

\( E^\circ_{\text{cell}} = E^\circ_{\text{cathode}} – E^\circ_{\text{anode}} \)

OR

\( E^\circ_{\text{cell}} = E^\circ_{\text{reduction}} – E^\circ_{\text{oxidation}} \)

Interpreting \( E^\circ \) Values:

• The more positive the standard reduction potential, the greater the substance’s tendency to gain electrons (be reduced).
• The more negative the value, the more readily the species loses electrons (gets oxidized).

Spontaneity and Feasibility:

• If \( E^\circ_{\text{cell}} > 0 \): the redox reaction is spontaneous in the forward direction.
• If \( E^\circ_{\text{cell}} < 0 \): the reaction is non-spontaneous (will only proceed in the reverse direction).

Visual Layout of a Galvanic Cell:

• Anode (oxidation): Electrons are released.
• Cathode (reduction): Electrons are accepted.
• Electrons flow: From anode to cathode in the external circuit.
• Salt bridge: Maintains charge neutrality by allowing ions to migrate.

Use of the Standard Hydrogen Electrode (SHE):

All standard electrode potentials are measured relative to the SHE, which is assigned an arbitrary value of \( E^\circ = 0.00\ \text{V} \).

IB Tip: You must always use values from the IB data booklet when answering questions. Don’t memorize E° values — refer to the booklet.