For the cell, Zn|Zn2+(1M)||H+(1M)|Pt(H2,1bar),E∘cell=0.74V and for the cell Pt(H2)|H+(1M)||Ag+(1M)|Ag,E∘cell=0.80V
Thus, the value of Ecell and spontaneity for the following reaction respectively are Ag|Ag+(0.1M)||Zn2+(0.1M)|Zn
A
1.44V and spontaneous
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B
0.4V and spontaneous
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C
−1.44V and non-spontaneous
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D
−1.53V and non-spontaneous
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Solution
The correct option is D−1.53V and non-spontaneous For the cell,
Zn|Zn2+(1M)||H+(1M)|Pt(H2,1bar)
E∘cell=E∘SHE−E∘Zn2+/Zn 0.74=0.00−E∘Zn2+/Zn ∴E∘Zn2+/Zn=−0.74V
Similarly, we can calculate the value of E∘Ag+/Ag: Pt(H2,1bar)|H+(1M)||Ag+(1M)|Ag E∘cell=E∘Ag+/Ag−E∘SHE ⇒E∘Ag+/Ag=0.80V
Now, for the cell Ag|Ag+(0.1M)||Zn2+(0.1M)|Zn E∘cell=E∘Zn2+/Zn−E∘Ag+/Ag=−0.74V−(0.80V)=−1.54V
Reaction quotient(Q)=[Ag+]2[Zn2+]=(0.1)2(0.1)=0.010.1=110 ∴Ecell=E∘cell−2.303RTnFlogQ
At, 298K,2.303RTF=0.0591V ∴Ecell=−1.54−0.05912log(110) =−1.54+0.05912log10 =−1.54+0.0295 =−1.51V Ecell<0, hence reaction is non-spontaneous.
So, (d) is correct.