|Is the pressure of H2 and O2
the same when
electrolysis takes place?|
|Question Date: 2013-05-08|
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:
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.
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.
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.
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