---
title: "Electrolysis: Half Equations at the Electrodes"
description: "A current through a molten ionic compound pulls it apart. Positive ions take electrons at the cathode and negative ions give them up at the anode, and each electrode gets its own half equation."
canonical: https://lightmysky.com/learn/science/electrolysis-half-equations-at-the-electrodes-mt_6FvxaD8wTY
source: https://lightmysky.com/learn/science/electrolysis-half-equations-at-the-electrodes-mt_6FvxaD8wTY.md
retrieved: 2026-09-12
---

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# Electrolysis: Half Equations at the Electrodes

A current through a molten ionic compound pulls it apart. Positive ions take electrons at the cathode and negative ions give them up at the anode, and each electrode gets its own half equation.

Subject: Science · Area: Matter & Materials · Ages 15 to 16
Page: https://lightmysky.com/learn/science/electrolysis-half-equations-at-the-electrodes-mt_6FvxaD8wTY

## Ready when they can

- Explains why an ionic solid does not conduct but the melt does
- Predicts the product at each electrode for a named molten compound
- Writes both half equations with the electrons balanced
- Combines the two half equations back into the overall reaction

## Lesson: Splitting melts with electricity

An ionic solid cannot conduct because its ions are locked in place. Melt it and the ions are free to migrate to the electrodes. A current then forces the compound apart, even though it would never split on its own. That forced split is electrolysis.

Positive cations drift to the negative cathode, and negative anions drift to the positive anode. At the cathode the cation gains electrons, which is reduction. At the anode the anion loses electrons, which is oxidation. For molten lead bromide, lead forms at the cathode and bromine forms at the anode.

**Example.** Each electrode gets its own half equation with atoms and charges balanced. Cathode: Pb2+ + 2e- -> Pb. Anode: 2Br- -> Br2 + 2e-. The two electrons gained match the two lost, so they cancel. The halves combine into PbBr2 -> Pb + Br2.

**Tip.** Write halves in this order: balance the atoms first, then balance the charges with electrons. Check that both halves move the same number of electrons. If they differ, scale one half up before combining.

**Recap.** Melt to free the ions, discharge cations at the cathode and anions at the anode, and balance each half.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Redox: Oxidation and Reduction as Electron Transfer](https://lightmysky.com/learn/science/redox-oxidation-and-reduction-as-electron-transfer-mt_NMTikR0FTM)
- [Testing for Ions and Gases](https://lightmysky.com/learn/science/testing-for-ions-and-gases-mt_PDZjzQJdVt)

## Opens up

- [Electrolysis of Solutions and Getting Reactive Metals Out of Ores](https://lightmysky.com/learn/science/electrolysis-of-solutions-and-getting-reactive-metals-out-of-ores-mt_l-t_JxRR7f)
- [Standard Electrode Potentials and Predicting Redox Reactions](https://lightmysky.com/learn/science/standard-electrode-potentials-and-predicting-redox-reactions-mt_LDI10CjoAI)
- [Cells That Do Work: Batteries, Fuel Cells and Corrosion](https://lightmysky.com/learn/science/cells-that-do-work-batteries-fuel-cells-and-corrosion-mt_NQQzlecX4v)