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Electricity from chemical change
Electromotive force (e.m.f.) ­ the `push' that a
cell is able to provide to a current flowing
through it (volts)
Standard electrode potentials (SEP) ­ the
potential difference of a half-cell relative to
the standard hydrogen electrode…read more

Slide 3

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Zn(s) Zn2+(aq) + 2e- oxidation
Cu2+(aq) + 2e- Cu(s) reduction
The electrochemical cell
The reaction releases energy A high-resistance voltmeter is
The zinc electrode decreases in used so that negligible current
(lost as heat) if the process is
mass but the copper electrode flows, and therefore the maximum
carried out in a single
increases potential difference is being
reaction vessel.
measured.…read more

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Half-cell notation
These should be
DOTTED lines…read more

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Ecell is directly proportional
to the total entropy change
in a reaction.
Reverse this
one!
Calculating the e.m.f.
Reverse the least positive value
Zn Zn2+ + 2e Eº = -0.76V
Cu2+ + 2e Cu Eº = +0.34V
Overall reaction: Cu2+ + Zn2+ Cu + Zn
Ecell= +0.34 ­ (-0.76) = 1.10V For a reaction to be feasible, the
Ecell value must be positive.
Once the value reaches about
+0.6V, the reaction is very likely
to progress.
REMEMBER: The e.m.f. is independent of the number of electrons being
transferred (so don't change the value when balancing equations!)…read more

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http://ibchem.com/IB/ibnotes/full/red_htm/19.1.htm…read more

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