professor Dave here let's talk about electrochemistry.
this should be a familiar object to everyone but how do batteries work? the first one was
invented by Alessandro Volta in 1800 and the chemistry hasn't changed too much
since then. the chemistry occurring in a voltaic cell is just a spontaneous
oxidation-reduction reaction which we now know is a transfer of electrons. the
only difference is that the oxidation and reduction half reactions are
physically separated from one another. the anode is where the oxidation takes
place and the cathode is where the reduction takes place
electrons captured in the oxidation then flow from the anode to the cathode which
generates a current of electrical energy which can be harvested to do work. each
side of the cell is called a half cell and they contain ions in solution. there
is also something called a salt bridge from which ions flow to maintain charge
balance
at the anode neutral zinc atoms give up two electrons to become zinc ions which
then fall off the electrode into solution. at the cathode copper ions in
solution near the electrode gain two electrons to neutralize and join the
copper lattice. ions in the salt bridge compensate for this gradual change in
overall charge
a voltaic or galvanic cell is one example of a kind of electrochemical
cell in which a spontaneous oxidation reduction reaction generates an electric
current. in an electrolytic cell an electric current drives an otherwise non
spontaneous reaction. when we describe the components of a voltaic cell we have
to use a particular notation. we list the oxidation half cell or the anode on the
left and the reduction half cell or the cathode on the right. the double vertical
lines represent the salt bridge that separates the half cells and single
vertical lines represent phase boundaries like between a solid
electrode and ions in solution. we can go between this electrochemical notation
and the balanced cell reaction by just including the number of electrons
involved in each half reaction
then use the least common multiple of electrons to combine the half reactions
into the cell reaction
and electrons will cancel. let's try to understand the concept of electron flow
just as water flows from high pressure to low pressure electrons flow from
areas of high to low electric potential. so electric potential is kind of like
electric pressure. potential difference is the difference in electric potential
between two points in the case of a voltaic cell those points would be the
anode and the cathode and their potential difference is called the cell
potential or Ecell, this will be expressed in volts. for a voltaic cell we
measure the cell potential by looking at the oxidation potential and the
reduction potential but since oxidation and reduction are reverse process these
will simply be the opposite of each other so we arbitrarily decided to
tabulate reduction potentials and Ecell for a voltaic cell will be
Ecathode minus Eanode because we are measuring the reduction that happens at
the cathode and then adding the reduction that could happen at the anode
but reversing the sign because it is actually oxidation that is taking place
so we have a whole list of reduction potentials and these numbers tell us how
favorable it is for a substance to be reduced
we can see here that fluorine is a very good oxidizing agent as it has a high
reduction potential which makes sense since fluorine has a very high electron
affinity. on the other end elements like lithium and sodium have very negative
reduction potentials making them good reducing agents since they have a
tendency to be oxidized as it is more favorable for them to lose an electron
than to gain one. to calculate Ecell for any hypothetical voltaic cell
containing two of these substances just calculate Ecathode
minus Eanode
the larger the Ecell value the greater the current the cell will
generate
the change in Gibbs free energy for the cell can be related to the cell
potential, this is the maximum work of a voltaic cell is capable of. here n is
the moles of electrons exchanged in the reaction and F is the Faraday constant
the electric charge of a mole of electrons. we can also relate cell
potential to its standard cell potential under standard conditions by using the
Nernst equation. here Q is the reaction question let's check comprehension
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