Non-Standard Conditions

AQA A-level ChemistryElectrochemistryLesson 9 of 14

The half equations are reversible reactions. The E^θ values depend on the position of equilibrium. Any factor that alters the position of equilibrium will alter the standard electrode potential in the direction predicted by Le Chatelier's principle. In the following equilibrium

MnO₄^-(aq) + 8H⁺ + 5e^- &rlhar Mn²⁺(aq) + 4H₂O(l)

The standard electrode potential E^θ is +1.52V. If the concentration of manganate (VII) ions or hydrogen ions is increased above 1.0 moldm^-3 the position of equilibrium will move to the right to counteract the change according to Le Chatelier's principle. Fewer electrons will be released and the electrode potential will become more positive than the standard value.

Key terms in this lesson

le chateliers principle

The principle that if a system at equilibrium is disturbed, the position of equilibrium shifts to counteract the change.

standard electrode potential

The e.m.f. of a half cell connected to a standard hydrogen half cell, measured under standard conditions with all solutions at 1 mol dm-3.

More in Electrochemistry

• The Standard Hydrogen Half Cell
• Standard Electrode Potential Eθ and the Electrochemical Series
• Calomel Electrode
• Standard Cell Potentials Eθcell Values and Electrochemical Cells
• Cell Diagrams
• Thermodynamic Feasibility of a Reaction and the Extent of a Reaction
• Electrochemical Cells
• Rechargeable Batteries

All 14 lessons in Electrochemistry · All AQA A-level Chemistry topics