14.33 (b)

[Andy Liao 1B]

Problem:
14.33 (a) The standard Gibbs free energy of formation of Tl3+(aq) is +215 kJ.mol-1 at 25°C. Calculate the standard potential of the Tl3+/Tl couple. (b) Will Tl+ disproportionate in aqueous solution?

I don't understand why in the solutions manual the equation of interest is 3Tl+(aq) -> 2Tl(s) + Tl3+(aq). Can someone please explain?

[sahiltelang-Discussion 1J]

They derive this equation by using Appendix 2B and coupling the half rxns for the oxidation and reduction of T1+.

[Dang Lam]

for part a, why did we have to flip the sign of delta G to negative instead of keeping it positive like given? Also how did they come up with the equation for part a?

[Farah Ahmad 2A]

You flip the sign of deltaG because the deltaG given is for the formation of Tl3+. The question asks for the standard potential of the Tl3+ /Tl couple, which when written like that indicates that Tl3+ is the reactant and Tl is the product, making it the flipped version of the formation of Tl3+. That is why we have to make +215 kJ/mol into -215kJ/mol.

[Dang Lam]

You flip the sign of deltaG because the deltaG given is for the formation of Tl3+. The question asks for the standard potential of the Tl3+ /Tl couple, which when written like that indicates that Tl3+ is the reactant and Tl is the product, making it the flipped version of the formation of Tl3+. That is why we have to make +215 kJ/mol into -215kJ/mol.

Got it! thank you