For which reaction is ΔH approximately (or exactly) equal to ΔU? A) H₂(g) + Br₂(g) → 2HBr(g) B) H₂O(l) → H₂O(g) C) CaCO₃(s) → CaO(s) + CO₂(g) D) 2H(g) + O(g) → H₂O(l) E) CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)

Question

Quizplus · Accepted Answer

The change in enthalpy (ΔH) is approximately equal to the change in internal energy (ΔU) for reactions occurring in the gas phase where there is no change in the number of moles of gas. In option A, both reactants and products are in the gas phase, and the number of moles of gas does not change (1 mole of H2 + 1 mole of Br2 gives 2 moles of HBr), making ΔH ≈ ΔU.

For Which Reaction Is ΔH Approximately (Or Exactly) Equal to ΔU