Consider the following unbalanced oxidation-reduct...

Question

Consider the following unbalanced oxidation-reduction reactions in aqueous solution:
l Ag⁺ (aq) + Li(s) → Ag(s) + Li⁺(aq)
Fe(s) + Na⁺(aq) → Fe²⁺(aq) + Na(s)
K(s) + H₂O(l) → KOH(aq) + H₂(g)

Based on the values you obtain for ΔH˚, which of the reactions would you expect to be thermodynamically favored? (That is, which would you expect to be spontaneous?)

Jules Bruno · Accepted Answer

A negative ΔH means the reaction is thermodynamically-favored (i.e. spontaneous).[readmore]For Ag+(aq) + Li(s) → Ag(s) + Li+(aq):∆Hrxn=∆Hf,Li+-∆Hf,Ag+∆Hrxn=-278.5-105.90=-384.4 kJ/molFor Fe(s) + Na+(aq) → Fe2+(aq) + Na(s):**add a coefficient of 2 to Na to balance the reaction:Fe(s) + 2 Na+(aq) → Fe2+(aq) + Na(s)∆Hrxn=∆Hf,Fe2+-∆Hf,Na+∆Hrxn=-87.6-2(-240.21)=392.82 kJ/molFor K(s) + H2O(l)  →  KOH(aq) + H2(g):**add a coefficient of 2 to K, H2O and KOH to balance the reaction:2K(s) + 2H2O(l)  →  2KOH(aq) + H2(g)∆Hrxn=∆Hf,KOH-∆Hf,H2O∆Hrxn=2(-482.4)-2(-285.83)=-393.14 kJ/molBased on the computed ΔH, the following reactions are spontaneous:Ag+(aq) + Li(s) → Ag(s) + Li+(aq)K(s) + H2O(l)  →  KOH(aq) + H2(g)

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