UCSB Science Line
 Is the pressure of H2 and O2 the same when electrolysis takes place? Question Date: 2013-05-08 Answer 1:When electrolysis takes place, the following reaction occurs: 2H2O → 2H2 + O2. Twice as much hydrogen as oxygen is produced. You can apply the ideal gas law, PV=nRT, to deduce that at a constant pressure such as 1 atmosphere you will produce twice the volume of hydrogen as oxygen. If you are electrolyzing water in an open environment, the gas produced will exist at 1 atmosphere of pressure. The pressure will be slightly higher if you use a setup like this: electrolysis-apparatus but that´s only because of the displacement of water. In the case of that apparatus, H2 would have a higher pressure because more gas would be produced and therefore more water would need to be displaced. Answer 2:There is twice as much H2 produced as O2 when water is electrolyzed. Accordingly, if you had fixed volume containers to collect the gases, you would expect the pressure of H2 to be twice that of O2. However, in real life, we often operate under conditions of fixed pressure, so you would expect the pressure of H2 to be the same as O2, but you'd get twice as much volume of H2. Answer 3: No - do the stoichiometry. There are twice as many atoms of hydrogen in water as there are of oxygen. There are the same number of atoms of hydrogen in a molecule of elemental hydrogen as there are atoms of oxygen in a molecule of elemental oxygen. Therefore there will be twice as many molecules of hydrogen as oxygen released by electrolysis. Thus, the pressure of hydrogen will be twice that of oxygen. Click Here to return to the search form.