$\ce{CH2CH2(g) + H2(g) -> CH3CH3(g)}$

Using this table, source: http://www.kentchemistry.com/images/links/Kinetics/TB08_003.GIF http://www.kentchemistry.com/images/links/Kinetics/TB08_003.GIF

C-C enthalpy = 348 kJ/mol
C-H enthalpy = 413 kJ/mol
H-H enthalpy = 436 kJ/mol

The way I see it, H-H has to break, C-C has to break, and then two C-H bonds have to form.

(Units omitted) Therefore, should the answer be: $413 \cdot 2 - 348 - 436 = 42 \, \text{kJ/mol}$

So then it has to be an endothermic reaction. Is this correct, or am I wrong?


Your reasoning is correct, but your numbers are wrong.

You are not breaking a C-C bond, but changing a C=C bond to C-C. So you will also need the energy for C=C which is 614 kJ/mol.

|improve this answer|||||

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.