Question

Use standard free energies of formation to calculate ΔG∘ at 25∘C for each of the following reactions.

1. CoO(s)+H2(g)→Co(s)+H2O(g)

2. NH4I(s)→HI(g)+NH3(g)

3.H2(g)+FeO(s)→Fe(s)+H2O(g)

4.SiH4(g)→Si(s)+2H2(g)

Answer 1

ΔG⁰ = ∑ΔG⁰_f (Products) - ∑ΔG⁰f (reactants)

Using this formula,

1) CoO(s) + H₂(g) ---------> Co(s) + H₂O(g)

ΔG⁰ = [ΔG⁰_f Co (s) + ΔG⁰_f (H₂O)] – [ΔG⁰_f CoO (s) + ΔG⁰_f H₂ (g)]

ΔG⁰ = [(0) + (-228.61)] – [(-214.2) + (0)]

ΔG⁰ = -14.41 kJ

==========================================================

2) NH₄I(s)→HI(g)+NH₃(g)

ΔG⁰ = [ΔG⁰_f HI (g) + ΔG⁰_f (NH₃ (g))] – [ΔG⁰_f NH₄I (g)]

ΔG⁰ = [(+1.3) + (-13.4)] – [-112 ]

ΔG⁰ = + 99.9 kJ [or + 100 KJ ]

========================================================

3) H₂(g)+FeO(s)→Fe(s)+H₂O(g)

ΔG⁰ = [ΔG⁰_f Fe (s) + ΔG⁰_f (H₂O)] – [ΔG⁰_f FeO (s) + ΔG⁰_f H₂ (g)]

ΔG⁰ = [(0) + (-228.61)] – [(−251.4) + (0)]

ΔG⁰ = + 22.79 kJ [or + 22.8 KJ]

============================================================

4) SiH₄(g)→Si(s)+2H₂(g)

ΔG⁰ = [ΔG⁰_f Si(s) + 2 ΔG⁰_f H₂(g) ] – [ΔG⁰_f SiH₄(g)]

ΔG⁰ = [ 0 + 2 x (0 )] – [+ 56.9]

ΔG⁰ = - 56.9 kJ [or + 57 KJ]

==============================XXXXXXXXXXXXXXXXXXXXXXX======================