Answer: 131 kJ/mol
ΔH=??
C2H6→C2H4+H2
Comparing the reactant and product, reactant has two extra C−H bond and a C−C bond. In product side we have one C=C bond and one H−H bond.
ΔH=[(EC−C+6EC−H)–(EC=C+4EC−H+EH−H)]
ΔH=[347+6×414]–(611+4×414+433]=2831−2700
ΔH=131 kJ/mol