Physical chemistryLesson 3 of 3 in the course Electrochemistry

Electrolysis: Cell Reactions, Aqueous Products, Electroplating, and Faraday Calculations

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

This lesson introduces electrolysis and explains how an external power source can drive a redox reaction that would not occur spontaneously. It also applies the basic ideas to the electrolysis of molten sodium chloride and water.

In a galvanic cell, a spontaneous redox reaction produces electrical energy that can do work in an external circuit. Electrolysis is the reverse kind of energy conversion: an external electrical source does work on a redox system and drives a reaction that is nonspontaneous under the conditions present.

All flashcards

Electrolysis
Use of electrical energy from an external source to drive a nonspontaneous chemical reaction.
Anode and cathode
Oxidation occurs at the anode; reduction occurs at the cathode.
Molten sodium chloride electrolysis
2NaCl(l)→2Na(l)+Cl2(g)\mathrm{2NaCl(l) \rightarrow 2Na(l) + Cl_2(g)}; sodium forms at the cathode and chlorine at the anode.
Water electrolysis
2H2O(l)→2H2(g)+O2(g)\mathrm{2H_2O(l) \rightarrow 2H_2(g) + O_2(g)}.
Electroplating
A process that deposits a thin metal layer on a conducting surface by reducing metal ions at the cathode.

Quiz questions

  1. During electrolysis of ordinary aqueous sodium chloride, which product forms at the cathode?Answer: Hydrogen gas, produced by reduction of water.
  2. Which products are associated with the industrial chlor-alkali process?Answer: Chlorine, hydrogen, and sodium hydroxide.
  3. In silver-plating a spoon, what are the roles of the spoon and silver electrode?Answer: The spoon is the cathode, and the silver electrode is the anode.
  4. How is the amount of electrons transferred calculated from charge?Answer: Divide the charge in coulombs by Faraday's constant.
  5. Why may standard electrode potentials alone fail to predict the observed products in aqueous sodium chloride electrolysis?Answer: Concentrations and practical electrode effects can influence which reactions occur.

Based on Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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