Catalysis in Redox system. 10Points

Only systems 1 and 2 might catalyse the reaction between peroxodisulphate(VI) and iodide ions.
S2O82-(aq) + 2I-(aq) → 2SO42-(aq) + I2(g)

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1. The system might catalyse the reaction.
3S2O82-(aq) + 2Cr3+(aq) + 7H2O(l) → 6SO42-(aq) + Cr2O72-(aq) + 14H+(aq) … (1a)
EcellΘ = (+2.01) - (+1.33) = +0.68 V > 0. The reaction (1a) is feasible.
6I-(aq) + Cr2O72-(aq) + 14H+(aq) → 3I2(aq) + 2Cr3+(aq) + 7H2O(l) … (1b)
EcellΘ = (+1.33) - (+0.54) = +0.79 V > 0. The reaction (1b) is feasible.
[(1a) + (1b)]/3 :
S2O82-(aq) + 2I-(aq) → 2SO42-(aq) + I2(g)
If both (1a) and (1b) are fast, the system can be a catalyst of the reaction.

2. The system might catalyse the reaction.
5S2O82-(aq) + 2Mn2+(aq) + 8H2O(l) → 10SO42-(aq) + 2MnO4-(aq) + 16H+(aq) … (2a)
EcellΘ = (+2.01) - (+1.52) = +0.49 V > 0. The reaction (2a) is feasible.
10I-(aq) + 2MnO4-(aq) + 16H+(aq) → 3I2(aq) + 2Mn2+(aq) + 8H2O(l) … (2b)
EcellΘ = (+1.52) - (+0.54) = +0.98 V > 0. The reaction (2b) is feasible.
[(2a) + (2b)]/5 :
S2O82-(aq) + 2I-(aq) → 2SO42-(aq) + I2(g)
If both (2a) and (2b) are fast, the system can be a catalyst of the reaction.

3. The system CANNOT catalyse the reaction.
S2O82-(aq) + Sn2+(aq) → 2SO42-(aq) + Sn4+(aq) … (3a)
EcellΘ = (+2.01) - (+0.15) = +1.86 V > 0. The reaction (3a) is feasible.
2I-(aq) + Sn4+(aq) → I2(aq) + Sn2+(aq) … (3b)
EcellΘ = (+0.15) - (+0.54) = -0.39 V > 0. The reaction (3b) is NOT feasible.
Since 3(b) is NOT feasible, the system CANNOT be a catalyst of the reaction.

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We can only predict that the system “might” catalyse the above redox reaction, but it is not sure. This is because we can only predict the feasibility of the catalytic reaction, but we do not know whether the rates are fast or slow. The system can catalyze the above reaction, only when reaction rates are fast.