Question

Calculate ΔGo and ΔSo at 25 oC for the following reactions.

2Al2O3 (s)  4Al (g) + 6O2 (g)

2H3AsO4  2As (g) + 4O2 (g) + 3H2 (g)

Answer 1

Reaction is

2Al₂O_3(s) 4Al_(g) + 6O_2(g)

Now For G⁰

G⁰ = Sum of G⁰_f of products - Sum of G⁰_f of rectants

= { 4 x G⁰_f of Al + 6 x G⁰_f of O₂ } - 2 x G⁰_f of Al₂O₃

= { 4 x 273 KJ/mol + 6 x 0 } - 2 x (-1576.4 KJ/mol)

= 2060.8 KJ

Now For S⁰

S⁰ = Sum of S⁰ of products - Sum of S⁰ of rectants

= { 4 x S⁰ of Al + 6 x S⁰ of O₂ } - 2 x S⁰ of Al₂O₃

= { 4 x 164.44 J/mol.K + 6 x 205.03 J/mol.K } - 2 x 50.986 J/mol.K

= 1785.968 J

Also for

2H₃AsO₄ 2As_(g) + 4O_2(g) + 3H_2(g)

G⁰ = Sum of G⁰_f of products - Sum of G⁰_f of rectants

= { 2 x G⁰_f of As + 4 x G⁰_f of O₂ + 3 x G⁰_f of H₂ } - 2 x G⁰_f of H₃AsO₄

= { 2 x 212.3 KJ/mol + 4 x 0+ 3 x 0 } - 2 x (-766) KJ/mol

= 1107.4 KJ

Now For S⁰

S⁰ = Sum of S⁰ of products - Sum of S⁰ of rectants

= { 2 x S⁰ of As + 4 x S⁰ of O₂ + 3 x S⁰ of H₂ } - 2 x S⁰ of H₃AsO₄

= { 2 x 174.1 J/mol.K + 4 x 205.03 J/mol.K+ 3 x 130.59 J/mol.K } - 2 x 184 J/mo.K

= 1192.09 J