How do you work this thermodynamics question out?

2016-06-25 6:39 pm
Find ∆Hc of propan-2-ol given that the following data.

∆Hf: CH3CH(OH)CH3(l) = –318, ∆Hc: C(s) = –394, H2(g) = –286 kJ mol-1

回答 (1)

2016-06-25 6:55 pm
Given :
3C(s) + 4H₂(g) + (1/2)O₂(g) → CH₃CH(OH)CH₃(l) ...... ΔH = -318 kJ
C(s) + O₂(g) → CO₂(g) ...... ΔH = -394 kJ
H₂(g) + (1/2)O₂ → H₂O(l) ...... ΔH = -286 kJ

Rewrite the three thermochemical equations as :
CH₃CH(OH)CH₃(l) →3C(s) + 4H₂(g) + (1/2)O₂(g) ...... ΔH = -(-318) kJ
3C(s) + 3O₂(g) → 3CO₂(g) ...... ΔH = 3(-394) kJ
4H₂(g) + 2O₂ → 4H₂O(l) ...... ΔH = 4(-286) kJ

Add the above three rewritten thermochemical equations, and cancel 3C(s), 4H₂(g) and (1/2)O₂(g) on the both sides.
CH₃CH(OH)CH₃(l) + (9/5)O₂(g) → 3CO₂(g) + 4H₂O(l) ...... ΔH = -2008 kJ

Hence, ΔHc[CH₃CH(OH)CH₃(l)] = -2008 kJ mol⁻¹


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