Does Le Chatelier's principle apply to electrochemical cells?

1 Answer

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.