Bond Dissociation Energy of Single, Double, Triple Bonds

[blazinfury]

I was looking in a book and I found that the Bond Energy of C-C

 

single bond= 347 KJ/mol

double bond= 614 KJ/mole

triple bond= 839 KJ/mole

 

Now this shows that a triple bond is stronger than a double which is stronger than a single bond. However, when I subtracted Bond Energies b/w the double and single bond, I got 267 KJ/mole, which is a value less than the energy of a single bond. When I did the same between a double and triple bond, I got 225 KJ/mole. From this, I get the impression that the single bond is the most energetic since it is the most stable, but why is it that as you increase the # of bonds (ie single--double--->triple), the energy of the addition of an extra single bond decreases? Does this imply that a triple is less stable than a double which is less stable than a single bond?

 

Also, since the energy difference between a triple and a double bond is 225 KJ/mole. Does this mean that if I add this amount of energy to a triple bond, it will break into a double bond, but to break the two pi bonds together, I would add 225+267 KJ/mole and convert the triple bond into a single bond?

 

Thank you.

[mississippichem]

I was looking in a book and I found that the Bond Energy of C-C

 

single bond= 347 KJ/mol

double bond= 614 KJ/mole

triple bond= 839 KJ/mole

 

Now this shows that a triple bond is stronger than a double which is stronger than a single bond. However, when I subtracted Bond Energies b/w the double and single bond, I got 267 KJ/mole, which is a value less than the energy of a single bond. When I did the same between a double and triple bond, I got 225 KJ/mole. From this, I get the impression that the single bond is the most energetic since it is the most stable, but why is it that as you increase the # of bonds (ie single--double--->triple), the energy of the addition of an extra single bond decreases? Does this imply that a triple is less stable than a double which is less stable than a single bond?

 

Also, since the energy difference between a triple and a double bond is 225 KJ/mole. Does this mean that if I add this amount of energy to a triple bond, it will break into a double bond, but to break the two pi bonds together, I would add 225+267 KJ/mole and convert the triple bond into a single bond?

 

Thank you.

 

A "single" bond is what's called a sigma-bond. They are more energetic than the pi-bonds that compose double and triple bonds. A double bond is one sigma-bond and one pi-bond. A triple bond is one sigma-bond and two pi-bonds.