1. In practice, the path independence of cell potentials is assumed so that we m
ID: 1027853 • Letter: 1
Question
1. In practice, the path independence of cell potentials is assumed so that we may calculate the potentials for net reactions by comparison of each half-reaction's reduction potential when coupled with the standard hydrogen electrode (S.H.E.). The following are reduction potentials versus S.H.E. under standard state conditions. Zn2+ + 2e- Zn Cu2+ + 2e- Cu Ag+ + e- Ag E' =-0.76 V E' = +0.34 V E' = +0.80 V Find the standard state cell potential for a Zn/Zn2t//Cu2 /Cu system. That is, the Zn/1.0 M Zn2+//1.0 M Cu2+/Cu system. 2. Recall that the driving force of a reaction can be altered by the concentrations of reactants and products as illustrated by the use of the equation In this equation, substitute-n78 for G and-n78" for G. Then solve the equation for E in terms of S and an adjustment factor (i.e., derive the general symbolic form of the Nernst equation).Explanation / Answer
1)
Given E0 of Zn (SRP) = -0.76V
E0 of Cu (SRP) = +0.34V
For the Galvanic cell ,the net reaction is
Zn + Cu+2 ------------> Zn+2 + Cu
Zinc is oxidised and Cu is reduced.
thus emf of the cell = reduction potential of Cu + oxidation potential of Zn
= reduction potential of Cu - reduction potential of Zn [ Oxidation potential of a metal = - its reduction potential]
Thus emf of galvanic cell = +0.34V - (-0.77V)
= 1.11V
2)delta G = delta G0 + RT ln Q
substituting- nFE
-nFE = -nFE0 + RTlnQ
E = E0 -[RT/nF]ln Q
Converting ln(natural logarithm) into log base 10
we get the common form of Nernst equation as
E = E0 -[RT/ 2.303nF]ln Q
3)
a) If the coefficients are changed, the n value changes and thus delta G value changes.
b) no change in E value with the coefficents of equation.
c) Delta G is an extensive property, as it changes with number of moles(coefficients of equation).
d) E is an intensive property, does not depned on the number of moles.
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