In which reaction would you expect ΔH to be substantially greater than ΔU (i.e., ΔH ΔU)? A) H₂(g) + Br₂(g) → 2HBr(g) B) CO₂(s) → CO₂(g) C) C₂H₂(g) + H₂(g) → C₂H₄(g) D) H₂O(s) → H₂O(l) E) HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

Question

In which reaction would you expect ΔH to be substantially greater than ΔU (i.e., ΔH > ΔU)? A) H₂(g) + Br₂(g) → 2HBr(g) B) CO₂(s) → CO₂(g) C) C₂H₂(g) + H₂(g) → C₂H₄(g) D) H₂O(s) → H₂O(l) E) HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

Quizplus · Accepted Answer

The difference between ΔH and ΔU is mainly due to the work done when gases are involved, especially in processes that involve a change in the number of moles of gas. Option B, the sublimation of CO2 from solid to gas, involves a significant change in volume and hence work done, leading to ΔH being substantially greater than ΔU.

In Which Reaction Would You Expect ΔH to Be Substantially