In: Chemistry
Consider the cell described below at 291 K:
Sn | Sn2+ (0.753 M) || Pb2+ (0.921 M) | Pb
Given EoPb2+→Pb = -0.131 V, EoSn2+→Sn = -0.143 V. Calculate the cell potential after the reaction has operated long enough for the Sn2+ to have changed by 0.325 mol/L.
anode reaction: oxidation takes place
Sn(s) -------------------------> Sn+2 (aq) + 2e- , E0Sn+2/Sn = - 0.143 V
cathode reaction : reduction takes palce
Pb+2(aq) + 2e- -----------------------------> Pb(s) , E0Pb+2/Pb = -0.44V
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net reaction: Sn(s) +Pb+2(aq) -------------------------> Sn+2 (aq) + Pb(s)
E0cell= E0cathode- E0anode
E0cell= E0Pb+2/Pb - E0Sn+2/Sn
= -0.131 - (-0.143)
= 0.012V
nernest equation
Ecell = E0cell -2.303RT/nF* log [Sn+2]/[Pb+2]
Here R= universal gas constant 8.314 J/K mol
T = absolute temperature =25(0C)= 298k
F= faraday = 96500 Coloumb/mol
n = no of moles of electrons are transfered =2
2.303RT/F= 0.0591
Ecell = E0cell -(0.0591/n)* log [Sn+2]/[Pb+2]
Ecell = 0.012 - (0.059 x1/2) *log [0.753/0.921]
Ecell = 0.0145 V
cell potential =Ecell = 0.0146 V