Monday, July 25, 2022

Water and air make hydrogen peroxide?

In this week's Chemical and Engineering News, this letter to the editor: 
Thermodynamics in hydrogen peroxide reaction

The question of whether water can form hydrogen peroxide should be answered by thermodynamics (see C&EN, June 13, 2022, page 3). If a reaction is possible (spontaneous), then the change in the Gibbs energy at constant temperature and pressure must be negative in sign. For the reaction of water with air (O2) to form hydrogen peroxide, the change in the Gibbs energy at standard temperature and pressure is positive (+116.78 kJ/mol for liquids or +136.25 kJ/mol for gases). Therefore, the production of hydrogen peroxide by reactions of water with oxygen is not possible for such laboratory conditions.

Thermodynamics never depends on any proposed reaction mechanisms, such as sprayed water droplets or the condensation of such water vapor on inert substrates.

Melvin H. Miles
St. George, Utah

Not quite sure what I think other than "gee, this seems really weird."  

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