Answer:
-1.9 KJ/mol
Explanation:
In order to solve the problem, we have to rearrange the equations in a way in which all molecules of O₂ and CO₂ are eliminated:
2C(diamond) + 2O₂(g) → 2CO₂(g) ΔH₁= 2 x (-395.4 KJ) ------> we multiply by 2 both reactants and products
2 CO₂(g) → 2CO(g) + O₂(g) ΔH₂= 566.0 KJ
CO₂(g) → C(graphite) + O₂(g) ΔH₃= -1 x (-393.5 KJ) ------> we use reverse rxn
2CO(g) → C(graphite) + CO₂(g) ΔH₄= -172.5 KJ
When we cancel the molecules that appear both in reactants and products, the total reaction is the following:
2C(diamond) → 2C(graphite)
ΔHt= ΔH₁ + ΔH₂ + ΔH₃ + ΔH₄ = 2 x (-395.4 KJ) + 566.0 KJ + (-1 x (-393.5 KJ)) - 172.5 KJ
ΔHt= 347.2 KJ
This is for 2 mol of C(diamond) which are converted in 2 mol of C(graphite). To obtain ΔH for the reaction of 1 mol C(diamond) to 1 mol (graphite) we have to divide into 2:
ΔH= -3.8 KJ/2mol= -1.9 KJ/mol
