4. (a) Calculate the Eo of a battery composed of reactions (ii) and (iii) : (b)

Question

4. (a) Calculate the Eo of a battery composed of reactions (ii) and (iii) :

(b) Calculate Go for this battery (reactions (ii) and (iii))

: (c) (0.4 pt) Calculate Keq for the battery reaction. (reactions (ii) and (iii))

6. Nernst equation. A battery is made from reactions (i) and (iii). Concentrations of solution phase species are given. Calculate the theoretical Emeasured for this battery. [CrO42] = 0.075 M [Cr3+] = 0.025 M [Cr2+] = 0.200 M

The half reactions Eo, volts vs. SHE (i)      Cr3+ +   e- --> Cr2+ - 0.408 (ii)     Cr3+   +   3 e- --> Cr (s) -0.744 (iii)    Ag2CrO4   +   2 e- --> 2 Ag(s)    +   CrO42- + 0.446 (iv)     Ag+   +   e - --> Ag (s) + 0.799 (v)     Ag2+    +   e- --> Ag + +1.980

Explanation / Answer

4

a)

for ii and iii

Ecell = Ered - Eox = 0.446 - -0.744 = 1.19 V

b)

dG = -nF*Ecell

n = 3*1 = 3mol of e-

F = 96500 C/mol

dG = -3*96500*1.19 = -344,505 J/mol = 344.505 kJ/mol

c)

Keq:

dG = -RT*ln(Keq)

Keq = exp(-dG/(RT))

Keq= exp(344505/(8.314*298)) = 2.445

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