Response:
ΔH = -793.6 kJ
Reasoning:
The ΔH for this particular reaction can be calculated through Hess's law, which allows one to combine the ΔH values of the half-reactions to find the overall ΔH:
The half-reactions are as follows:
1) H₂(g) + ¹/₂O₂(g) ⟶ H₂O(g) ΔH₁ = −241.8 kJ
2) X(s) + 2Cl₂(g) ⟶ XCl₄(s) ΔH₂ = +356.9 kJ
3) ¹/₂H₂(g) + ¹/₂Cl₂(g) ⟶ HCl(g) ΔH₃ = −92.3 kJ
4) X(s) + O₂(g) ⟶ XO₂(s) ΔH₄ = −639.1 kJ
5) H₂O(g) ⟶ H₂O(l) ΔH₅ = −44.0 kJ
The calculation involves summing (4) + 4×(3) - (2) - 2×(1) - 2×(5):
(4) X(s) + O₂(g) ⟶ XO₂(s) ΔH = −639.1 kJ
+4×(3) 2H₂(g) + 2Cl₂(g) ⟶ 4HCl(g) ΔH = −369.2 kJ
-(2) XCl₄(s) ⟶ X(s) + 2Cl₂(g) ΔH = -356.9 kJ
-2×(1) 2H₂O(g) ⟶ 2H₂(g) + O₂(g) ΔH = +483.6 kJ
-2×(5) 2H₂O(l) ⟶ 2H₂O(g) ΔH = +88.0 kJ
= XCl₄(s) + 2H₂O(l) ⟶ XO₂(s) + 4HCl(g)
<pThus, ΔH is:
ΔH = -639.1 kJ -369.2 kJ -356.9 kJ +483.6 kJ +88.0 kJ
ΔH = -793.6 kJ
I trust this clarifies things!