25. Galvanic Cell

version from 2016-01-27 17:44

Section

1. A galvanic cells is where chemical energy becomes electrical energy
2. It is created when an electrode of a metal is submerged into a solution of its own ions.
3. An equilibrium is formed at the surface of the metal electrode, whereby the metal releases some metal ions,
and retains some free electrons. When the free electron amount gets high enough within the electrode, no more
metal ions are released as the negative charge is preventing the loss of any more positive charge.
4. If 2 electrodes are connected by a wire that can conduct electrons, the electrons will move to where they are
in shorter supply...
5. The electrode with more electrons will be more negative, taking up positive metal ions from the solution, and
growing in size. The resulting electromotive force is determines by the difference between the two voltages of
the electrodes.
6. In a cell, a resting potential is generated when there is a high concentration of K+ and Cl- on one side of a
semi-permeable (only to K+) membrane, and a low concentration of K+ and Cl- on the other side. Naturally, the
K+ will move through to where it is deficient, until the concentration of Cl- become so high (as it can't pass thru)
that no more K+ can get through. You may also stop K+ by putting an equal, but opposite voltage on the other
side of the membrane, making it so positive that the K+ is repelled and does not enter.
7. To calculate the electromotive voltage of this diff. in membranes, there is:

The Nernst Equation

UElectric Potential Energy
FFaraday Constant (Charge of 1 mol of electrons)
zCharge of ion expressed in multiples of elementary charge
lnlog subscript e
c/c*can be randomly selected, equilibrium voltage on membrane then corresponds to membrane

8. Both solutions will be electroneutral, because everything takes place on the surface.

REMEMBER! The ANODE will LOSE electrons
The CATHODE will GAIN electrons
The CATION is the positive ion
The ANION is the negative ion