How to Calculate Enthalpy Change using Given Data

Question:

When 26.7 g of H₂S was burned in excess oxygen, 406 kJ was released. What is ΔH for the following equation?

2H₂S(g) + 3 O₂(g) → 2SO₂(g) + 2 H₂O(g).

a. 159 kJ
b. 406 kJ
c. -159.3 kJ
d. -406 kJ

Answer:

The correct answer is option C. The enthalpy change for the given equation is -159 kJ/mol.

Explanation:

The enthalpy change (∆H) for the given equation can be calculated using the given information. First, we need to determine the number of moles of H₂S burnt. The molar mass of H₂S is 34.08 g/mol (2(1.008 g/mol) + 32.06 g/mol), so the number of moles is 26.7 g / 34.08 g/mol = 0.78 mol. Next, we calculate the ∆H using the balanced equation and the energy released: 0.78 mol * (-406 kJ) / 2 mol H₂S = -159 kJ/mol. Therefore, the correct answer is option c. -159.3 kJ.

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