A) use bond enthalpies to estimate the enthalpy change for the reaction of hydrogen with ethene.

h2(g) + c2h4(g) c2h6(g)

ans: kj

(b) calculate the standard enthalpy change for this reaction using heats of formation.

ans:

(a) -134 kJ         (b) -136 kJ

Explanation:

a) Using the accounting of the  enthalpy  of broken and formed  bonds we will have the answer for this question ( remember the enthalpy of bonds broken are positive and those formed are negative)

ΔHrxn(kJ) = 6H (C-H) + 1 (C-C)+ 1H (H) + 1(C=C) + 4(C-H)

= 6(-411) +(-346) +432 + 602 + 4(411)

= - 134 kJ

(b) ΔHrxn = ΔHºf(C2H6) - ΔHºf (C2H4) = -83.75 kJ- 52.3 kJ =  -136 kJ

( ΔHºf (H2)) = 0)