Question

Determine which of the following pairs of reactants will result in a spontaneous reaction at 25°C.

A.) Zn(s)+Na+(aq)

B.) Cr3+(aq)+Ni(s)

C.) Sn4+(aq)+Mg(s)

D.) Cd(s)+Ba2+(aq)

E.) none of these

Answer 1

using reduction potential value we can decide which is spontaneous. If the species
with higher reduction potential undergoes reduction ,then the reaction will be
spontaneous

A.) Zn(s)+Na+(aq)
overall reaction will be
Zn(s)+Na+(aq)---> Zn2+ + Na
Na+ /Na(s)   −2.71
Zn2+ /Zn(s)   −0.76
since Zn has higher redudtion potential,it must undergo reduction.But in the reaction
given above Zn is undergoing oxidation.
Hence non spontaneous
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B.) Cr3+(aq)+Ni(s)
Cr3+ /Cr(s)   −0.74
Ni2+/   Ni(s)   −0.25
Ni has higher reduction potential, but in the reaction Ni undergoes oxidation
Hence non spontaneous
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C.) Sn4+(aq)+Mg(s)
Sn4+ /Sn2+   +0.15
Mg2+ /Mg(s)   −2.372
Sn has higer reduction potential than Mg . it will undergo reduction
In the given reaction Sn4+ undergoes reduction

Hence this reaction is spontaneous
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D.) Cd(s)+Ba2+(aq)

Cd2+ /Cd(s)   −0.40
Ba2+ /Ba(s)   −2.912
Non spontaneous
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