Question

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1. Determine the value of the standard free energy, ΔG^o, in kJ/mol at 25^oC for the reaction: Na⁺_(aq) + 2Br ^-_(aq)   →   Na_(s) + Br_2(g)

ΔG^o = ?

2. Determine the value of the standard free energy, ΔG^o, in kJ/mol at 25^oC for the reaction: Al³⁺_(aq) + Ca_(s)   →   Al_(s) + Ca²⁺_(aq)

ΔG^{o = ?}

Answer 1

Hi,

1. 2Na+(aq) + 2Br -(aq)   → 2Na(s) + Br2(g) (balanced reaction)

oxidation, 2Br -(aq) + 2e^– Br2(g) E1 (reduction potential)= +1.066 V

Reduction,2Na⁺(aq) + 2e^–   2Na(s) E2 (reduction potential)= -2.714 V

Eocell= E1-E2= (-2.714)- 1.066 = -3.78 V

ΔGo = -nFEocell

ΔGo= -2*96500*( -3.78 )= 729540 J= 729.540 kJ, which means reaction is not feasiable.

The next problem can similarly be solved by using the following data.

Al³⁺(aq) + 3 e^–   Al(s) -1.66

Ca²⁺(aq) + 2 e^–   Ca(s) -2.87