Chemistry help?

Question

http://www.uccs.edu/Documents/chemistry/nsf/106%20Expt9V-GalvanicCell.pdf

2) as a standard voltaic cell runs,  the voltage delivered by the cell drops with time. Why does this happen?

Answer 1

All the oxidation and reduction reactions takes place in Standard voltaic cell.

Nernst Equation :

Nernst equation is , where is the reaction quotient.

As the voltage drop in the cell decreases with time then reduces, decreasing emf of the cell.

When the oxidizer pulls electrons with a stronger electromotive force, that voltage for a standard cell decreases, reducing the emf.

Hence as the voltage drop by the cell decreases with time, emf of the cell goes down.