Q. Assume each reaction is carried out in an open container. For which reaction will ΔH = ΔE ?
A) H₂(g) + Br₂(g) → 2HBr(g)
B) C(s) + 2H₂O(g) → 2H₂(g) + CO₂(g)
C) PCl₅(g) → PCl₃(g) + Cl₂(g)
D) 2CO(g) + O₂(g) → 2CO₂(g)
Explanation
[Solution from source] ΔH = ΔE + Δn_gRT, so ΔH = ΔE only when the number of moles of gas is unchanged. For H₂ + Br₂ → 2HBr, Δn_g = 2 − 2 = 0. The water-gas reaction and the PCl₅ decomposition have Δn_g = +1, and the CO combustion has Δn_g = −1. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.