Calculate the standard enthalpy of formation of C₂H₅OH(l) at 298 K from the following data (all at 298 K):
(i) C(s) + O₂(g) → CO₂(g); ΔH = -394 kJ
(ii) H₂(g) + 1/2 O₂(g) → H₂O(l); ΔH = -286 kJ
(iii) C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l); ΔH = -1367 kJ

Question

Calculate the standard enthalpy of formation of C₂H₅OH(l) at 298 K from the following data (all at 298 K):

(i) C(s) + O₂(g) → CO₂(g); ΔH = -394 kJ

(ii) H₂(g) + 1/2 O₂(g) → H₂O(l); ΔH = -286 kJ

(iii) C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l); ΔH = -1367 kJ

TestHub · Accepted Answer

Target: 2C(s) + 3H 2 (g) + 1/2O 2 (g) → C 2 H 5 OH(l). Take 2(i) + 3(ii) - (iii): ΔH = 2(-394) + 3(-286) - (-1367) = -788 - 858 + 1367 = -279 kJ/mol. This is option (a).

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