Which of the following equations represents the enthalpy of combustion of propane? A C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(l) B C₃H₈(g) + \rac{7}{2}O₂(g) → 3CO₂(g) + 4H₂O(l) C C₃H₈(g) + 3O₂(g) → 3CO₂(g) + 4H₂O(g) D C₃H₈(g) + \rac{3}{2}O₂(g) → 3CO₂(g) + 4H₂O(g) - Scottish Highers Chemistry - Question 16 - 2016

To determine the enthalpy of combustion for propane (C₃H₈), we need to identify the reaction where propane reacts with oxygen to produce carbon dioxide and water. The enthalpy of combustion reflects the complete combustion of propane with the appropriate stoichiometric coefficients.

Let's analyze the options:

• Option A: C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(l)

  • This equation matches the balanced combustion for propane with liquid water as a product.

• Option B: C₃H₈(g) + \rac{7}{2}O₂(g) → 3CO₂(g) + 4H₂O(l)

  • This equation is also valid since it balances the same reaction using a fraction for oxygen, which is acceptable in stoichiometry.

• Option C: C₃H₈(g) + 3O₂(g) → 3CO₂(g) + 4H₂O(g)

  • This option shows water vapor as a product.

• Option D: C₃H₈(g) + \rac{3}{2}O₂(g) → 3CO₂(g) + 4H₂O(g)

  • Similar to Option C, it features water in vapor form.

Despite options B, C, and D being correctly balanced, the standard representation of the enthalpy of combustion typically uses liquid water as in option A.