Question Detail
Question
Given the following reactions and their enthalpy changes: C(s) + O₂(g) → CO₂(g) ΔH = -393.5 kJ, H₂(g) + ½O₂(g) → H₂O(l) ΔH = -285.8 kJ, CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l) ΔH = -890.3 kJ. Calculate ΔH for the reaction: C(s) + 2H₂(g) → CH₄(g).
Correct Answer
Option A is the correct answer.
Detailed Explanation
Using Hess's law: Target = CO₂ + 2H₂O - (CH₄ + 2O₂). Actually, combine: (C + O₂ → CO₂) + 2(H₂ + ½O₂ → H₂O) - (CH₄ + 2O₂ → CO₂ + 2H₂O) = C + 2H₂ → CH₄. ΔH = (-393.5) + 2(-285.8) - (-890.3) = -393.5 -571.6 + 890.3 = -74.8 kJ.
Hint
Use Hess's law to manipulate the given equations to sum to the desired reaction.