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Chapter 21 Lecture 6

# Chapter 21 Lecture 6 - Electrolysis of water Pure water is...

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Electrolysis of water Pure water is hard to electrolyze (low conductivity), – so a small amount of a non-reactive salt (NaNO 3 ) is added (can be neglected) 0 on pontaneous reaction 21-80 E cell < 0 ֜ non spontaneous reaction ֜ To drive the reaction, the external voltage must be greater than 1.24 V

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Overvoltage vervoltage he extra voltage (in the case of water over 1.24) O e o tage t e e t a o tage ( t e case o ate o e ) needed to drive the reaction – Due to kinetic factors: such as the large activation energy required for gases to form at the electrode qg •F o r H 2 O on most inert electrodes, the overvoltage is 0.4 to 0.6 V per electrode athode reduction: = 42 6 0V Cathode, reduction: E = 0.42 0.6 1.0 V Anode, oxidation: E = +0.82 + 0.6 +1.4 V Total: E cell = -1.0 – (+1.4 ) -2.4 V 21-81
Electrolysis of aqueous solutions Example : Predict the products of the electrolysis of a mixture of 1M NaCl( aq ) and 1M KNO ( aq ) with Possible cathode half-reactions (reduction) – 1. Reduction of H 2 O ( q ) 3 ( q ) inert electrodes at pH = 7.

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Chapter 21 Lecture 6 - Electrolysis of water Pure water is...

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