Answer to Question #329714 in Chemistry for grey tyrant

Question

Calculate the  ΔG° using Hess Law for the reaction: Cu2S(S) + O2(g) ( Cu(s) SO2(g)

2 Cu(s) + S(s)  ( Cu2S(L) Δ    Go  = -86.2 kJ

S(s)  +  O2(g)  (  SO2(g) Δ        Go = -300.1 kJ

Answer 1

Cu₂S(s) + O₂(g) → 2Cu(s) + SO₂(g), ΔG°_x = ???

eq = equation

(1^st eq): 2Cu(s) + S(s) → Cu₂S(s), ΔG°₁ = −86.2 kJ

(2^nd eq): S(s) + O₂(g) → SO₂(g), ΔG°₂ = −300.1 kJ

Solution:

According to Hess's law, the heat of reaction depends upon Initial and final conditions of reactants and does not depend of the intermediate path of the reaction.

1) Modify the two given equations to get the target equation:

(1^st eq): flip it so as to put Cu₂S(s) on the reactant side.

(2^nd eq): do nothing. We need one mole of SO₂(g) on the product side and that's what we have.

2) Rewrite the two equations with the changes made:

(1*^st eq): Cu₂S(s) → 2Cu(s) + S(s), ΔG°₁* = +86.2 kJ

(2^nd eq): S(s) + O₂(g) → SO₂(g), ΔG°₂ = −300.1 kJ

Thus, adding modified equations and canceling out the common species on both sides, we get:

Cu₂S(s) + O₂(g) → 2Cu(s) + SO₂(g)

3) Add the ΔG° values of (1*^st) and (2^nd) equations to get your answer:

ΔG°_x = ΔG°₁* + ΔG°₂ = +86.2 kJ + (−300.1 kJ) = −213.9 kJ

ΔG°_x = −213.9 kJ

Answer: The ΔG° for the reaction is −213.9 kJ