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Half-equations and HT skills for electrolysis

Chemical changes • Electrolysis

Key concepts

What you'll likely be quizzed about

  • A half-equation describes either oxidation or reduction at a single electrode.
  • It shows the chemical species that lose or gain electrons, isolating the electron transfer for that electrode.
  • The complete cell reaction combines the two half-equations, with electrons cancelling out.
  • Half-equations explicitly use electrons to balance charge.
  • In oxidation, electrons appear on the product side, while in reduction, they appear on the reactant side.
  • The presence and quantity of electrons indicate the change in oxidation state for the involved element.

Flashcards

Test your knowledge with interactive flashcards

What is the half-equation for oxide ion oxidation in molten oxide electrolytes?

Click to reveal answer

2O2− → O2 + 4e−.

Key notes

Important points to keep in mind

Electrons appear on the product side for oxidation and on the reactant side for reduction.

Always balance charge after balancing atoms; electrons adjust charge balance.

Use H2O and H+ in acidic solutions and H2O and OH− in alkaline solutions to balance O and H.

Multiply half-equations so electrons cancel before adding them to get the full cell reaction.

Identify whether the electrolyte is aqueous or molten to determine competing water reactions.

Inert electrodes do not change the species available for electrode reactions.

Check oxidation states to decide how many electrons are required.

Count atoms and charge as the final verification step for any completed half-equation.

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