Changes in Q

[eduardomorales5]

If we decreased the concentration of a reactant, what would happen to the cell potential of the cell? If we decreased the mass of a reactant, what would happen to the cell potential?

[Sanjana Munagala_1j]

Generally these questions are applicable to concentration cells. When I approach such problems, I think about the concentration difference between the two cells. If reducing the concentration of one half cell will reduce the concentration difference between the two half cells, then E cell will decrease, and vice versa. You can also look at this in terms of how it affects Q and relate it to the Nernst equation, to get a more quantitative value for the change. When you ask about mass, I am assuming you are talking about the mass of the metal electrodes. In this case, you need to remember that neither concentration of the solution nor Q is affected by the metal electrode's mass and therefore changing the mass will not affect E cell.

Hope that helps!

[Rohit Ghosh 4F]

Yes, by looking at the Nernst equation, you can see that mass is never factored into the final calculation, while concentration definitely is. As such, diluting the solution will change the final answer you obtain, but changing the mass of the electrode will not.

[Tyler Angtuaco 1G]

Reducing the concentration of the reactant results in a higher Q value. Based on the Nernst equation, this would result in a lower cell potential.