Avoltaic cell is created using a zinc electrode immersed in a1.0 m solution of zn+2 ions and a silver electrodeimmersed in a solution of 1.0 m ag+ ions. the twoelectrodes are connected with a wire, and a salt bridge is palcedbetweenthe two half-cells. the temperature of the cells is25oc.
1: what is the balanced half-reactions that are occurring atthe cathode and the anode.
2: calculate the standard cell voltage for the cell.
3: calculate δg0 for the cell.
4: how will the voltage be affected if 2.5 g of kcl is addedto each half cell? justify your response.

1: Anode:        Zn    ⇒    Zn²⁺ + 2e

  Cathode:   2Ag ⁺ +  2e⁻    ⇒ 2Ag⁻

2: 1.56 V

3:  -3.01 x 10⁵ J

4: Decrease

Explanation:

From a reference table we can get the standard reduction potentials:

Ag ⁺ +  e⁻    ⇒ Ag     Eº =  0.80 V

Zn²⁺ + 2 e⁻ ⇒ Zn      Eº = -0.76 V

The  Ag will be reduced since it has the more positive standard reduction potential, and Zn will be oxidized.

The balanced half reactions are:

Zn  ⇒    Zn²⁺ + 2e⁻ (anode where oxidation occurs)  Eº = - (-0.76 V)= +0.76V

2Ag ⁺ +  2e⁻    ⇒ 2Ag     Eº =  0.80 V (cathode /reduction)  Eº = 0.80 V

Note the reversal of sign for the Zn half cel,l and that even though we multiplied the Ag half cell by 2 to balance, we dont do the same with the reduction potential since it is an  intensive property.

The standard cell voltage will be given by:

Eºcell = Eº anode + Eº cathode = + 0.76 V + 0.80 V = 1.56 V

Please be careful with this formula since there are texts that write it as Eºcell= Eº cathode - Eºanode  which is equivalent since this will reverse the sign we did previously.

ΔGº = - nFEº where

n= number of moles of electrons  electrons exchanged ,

F= Faraday constant, 96500 Coulombs/ V mol e⁻,

Eº = the standard cell voltage

ΔGº = - 2 mol e⁻ x 96500 coulombs/ V mol e x  1.56 V =  -3.01 x 10⁵ J

To answer part 4 we need to remember that what we are doing is effectively adding the chloride ions to the half cells, and that the solubilty of silvel chloride is extremely low. Therefore some of the Ag⁺ ions will be precipitated, and the cell voltage will decrease.