Which of the following reactions should have the larger emf under standard conditions? Why? CuSO4(aq)+Pb(s) ⇌ PbSO4(s)+Cu(s)
Cu(NO3)2(aq)+Pb(s) ⇌ Pb(NO3)2(aq)+Cu(s)

Cu(NO3)2(aq)+Pb(s) ⇌ Pb(NO3)2(aq)+Cu(s)

Explanation:

If we look at the both reactions closely, we will quickly discover that the reaction CuSO4(aq)+Pb(s) ⇌ PbSO4(s)+Cu(s) involves PbSO4.

The compound PbSO4 is insoluble in water and sinks to the bottom of the reaction vessel. When this occurs, the concentration of Pb^2+ becomes low. This will bring about a low voltage in the cell.

On the other hand, Pb(NO3)2 is soluble in water hence the cell voltage in this case is higher than the former.