Question

∆U^θof combustion of methane is – X kJ mol^–1 . The value of ∆H^θ is

(i) = ∆U^θ

(ii) > ∆U^θ

(iii) < ∆U^θ

(iv) = 0

Answer 1

Since ∆H^θ = ∆U^θ + ∆n_gRT and ∆U^θ = –X kJ mol^–1 , 

∆H^θ = (–X) + ∆n_gRT. ⇒ ∆H^θ < ∆U^θ 

Therefore, alternative (iii) is correct.