Calculate the standard enthalpy of reaction for: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l), given ΔH°f [CH₄(g)] = -75 kJ/mol, ΔH°f [CO₂(g)] = -394 kJ/mol, and ΔH°f [H₂O(l)] = -286 kJ/mol.
Answer and explanation
Correct answer: B. -891 kJ/mol
- Step 1: Apply Hess's law: . Note .
- Step 2: Compute: .
Answer
-891 kJ/mol.
Why not the others: -605 kJ/mol omits one water molecule; +891 kJ/mol inverts the algebraic sign; -966 kJ/mol neglects reactant methane enthalpy.
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