Question

Does Le Chatelier's principle apply to electrochemical cells?

Answer 1

Le Chatelier's Principle is very important when applied to electrochemical cells.

Consider the Daniel Cell:

The 2 half cells are:

`Zn^(2+)+2erightleftharpoonsZn` `E^(o)=-0.76"V"`

`Cu^(2+)+2erightleftharpoonsCu` `E^(0)=+0.34"V"`

To find `E_(cell)^(0)` you subtract the least positive value from the most positive value:

`E_(cell)^(0)=+0.34-(-0.76)=+1.1"V"`

And the cell reaction is therefore:

`Zn+Cu^(2+)rarrZn^(2+)+Cu`

These refer to standard conditions i.e unit concentrations, 298K and pH zero.

What would happen if we were to reduce the concentration of `Cu_((aq))^(2+)` from `1"mol/l"` to `0.1"mol/l"` ?

Looking at the Cu2+/Cu half - cell Le Chatelier's Principle would predict that would cause the position of equilibrium to shift to the left to produce more Cu2+.

This would cause the `E^(0)` value to become less positive. This would therefore reduce the potential difference between the 2 half - cells and therefore the value of `E_(cell)`.

We can calculate the new value using the Nernst Equation which in this case is:

`E_(cell)=E_(cell)^(0)-(0.0591)/(2)log([[Zn^(2+)]]/([Cu^(2+)]))`

`E_(cell)=1.1-(0.0591)/(2)xx1`

`E_(cell)=+1.07"V"`

So as predicted by Le Chatelier,. the value of `E_(cell)` has been reduced.