n thermodynamics, we determine the spontaneity of a reaction by the sign of G. I
ID: 974824 • Letter: N
Question
n thermodynamics, we determine the spontaneity of a reaction by the sign of G. In electrochemistry, spontaneity is determined by the sign of Ecell. The values of G and Ecell are related by the following formula: G=nFEcell where n is the number of moles of electrons transferred and F=96,500J/Vmol e is the Faraday constant.
Part A
The standard reduction potentials of lithium metal and chlorine gas are as follows:
In a galvanic cell, the two half-reactions combine to
2Li(s)+Cl2(g)2Li+(aq)+2Cl(aq)
4.40 V
Part B
Calculate the free energy G of the reaction.
Reaction Reduction potential(V) Li+(aq)+eLi(s) 3.04 Cl2(g)+2e2Cl(aq) +1.36
Explanation / Answer
Solution:
part A)
Ecell = E(Reduction) + E(Oxidation)
standard reduction potentials are given for both the half cells. from over all cell reaction, oxidation of Li is taking place. Oxidation potential = - (reduction potential)
hence, oxidation potential of Li = -(-3.04V) = +3.04 V
Ecell = 1.36 V + 3.04 V = 4.04 V
part B)
G=nFEcell
from part A) Ecell = 4.04 V
two moles of electrons are transferred in the balanced equation. So, n = 2 mole e-
plug in the values in the equation,G=nFE
G = - (2 mol e-) ( 96,500J/Vmol e) (4.40 V)
G = -849200 J
Or, G = -849.2 kJ (Answer)
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