निम्न अभिक्रिया की एन्थैल्पी की गणना कीजिये ।
`CH_(2) = CH_(2)(g) + H_(2)(g) rarr CH_(3)-CH_(3)(g)`
`C-H, C-C,C=C` तथा `H-H` आबंधो की आबन्ध ऊर्जाऐ क्रमश : `414,347,615` और `425 kJ mol^(-1)` हैं।

Explanation

दी गयी अभिक्रिया निम्न है -
`CH_(2) = CH_(2)(g) + H_(2)(g) rarr CH_(3) - CH_(3)(g), Delta_(r)H = ?`
चूँकि, Enthalpy change of a reaction = [Energy required to break the bonds in the molecules of reactions]-[Energy released in the formation of bond in the molecules of products]
अतएव,
`Delta_(r)H = sumB.E._("(reactions)") - sumB.E._("(product)")`
`= [4 xx (B.E. "of" C-H) + 1 xx(B.E. "of" C=C) + 1 (B.E. "of" H-H)] - [6xx(B.E. "of" C-H) + 1 xx (B.E. "of" C-C)]`
`= [4 xx 414 + 1 xx 615 + 1 xx 435] - [6 xx 414 + 1 xx 347] = [2706] - [2831]`
`= -125`kJ.