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As an example, if a given amount of electricity releases
5 g of H2 gas
when passed through an electrolysis cell for the decomposition
of water, then twice as much electricity will produce
10 g of hydrogen gas.
Furthermore, if enough electricity is passed through
the cell to yield 2 g of H2
gas at the cathode,
then 16 g of O2
gas will be released at the anode.
These numbers are easily recognizable as representing
1 mole of H2 and 1/2 mole of O2,
which are the relative proportions
in which these gases combine to form H20.
In Faraday's time, his experiments were a remarkable
set of observations that helped to establish the principles
of chemical combination.
Today they are self-evident consequences of the theory
that electrons form chemical bonds.
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We have referred to Faraday's constant
previously as representing one mole of electrons, and have
used it in the form
F = 23.056 kcal mol-1
eV-1
It is more convenient in electrolysis experiments to express
F in coulombs, the customary unit of electrical charge.The
charge on an electron is 1.6021 x 10-19
coulomb, so one mole of electrons will have a total
charge of
1.6021 x 10-19 coulomb
x 6.022 x 1023 mol-1 =
96,487 coulombs mol-l
Passing 96,487 coulombs of electricity through a cell means
sending one mole of electrons from one electrode to the other,
with the corresponding chemical changes.
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