KEAM 2012 Physics and Chemistry Paper

The reaction for which ∆ng≠0,‌‌∆H≠∆U because ∆H=∆U+∆ngRT
∆ng=nP−nR
(where, np and nR represent the number of moles of gaseous products and reactants respectively.)
(a) C(graphite) +O2(g)⟶CO2(g);
∆ng=np−nR=1−1=0
(b) C2H4(g)+H2(g)⟶C2H6(g)
∆ng=1−2=−1
(c) 2C( graphite )+H2(g)⟶C2H2(g);
∆ng=1−1=0
(e) N2(g)+O2(g)⟶2NO(g)
∆ng=2−2=0
Thus, for the reaction given in option (b), ∆H≠∆U