bond strength

[inaccensa]

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Bond Strength ---> lowest to highest C-C<C=C<C(triple)C

Bond dissociation energy ---> lowest to highest C-C <C=C< C(triple)C

So bond strength increases as the distance betwen the atom decreases,so there is a inverse proportion? 😕

The energy required to break a triple bond is higher than the energy req for single, so the bond strength is directly proportional to the bond dissociation energy.

Can anyone explain the criteria for bond energy & alkane is more stable than alkene and alkyne. I'm not talking about the bond strength, but the stability of the overal molecule. This is all soo confusing!!

 

[RogueUnicorn]

bond strength DIRECTLY results in the stability of the molecule.

 

[inaccensa]

bond strength DIRECTLY results in the stability of the molecule.

Are you saying alkynes are the most stable?

 

[RogueUnicorn]

yes as long as we're talking only about the stability of the c-c link. the entire molecule's stability would be contigent on the C-H bonds as well. i have a feeling that C2H6 is more stable as a whole than C2H2 due to the additinal CH bonds.

 

[inaccensa]

yes as long as we're talking only about the stability of the c-c link. the entire molecule's stability would be contigent on the C-H bonds as well. i have a feeling that C2H6 is more stable as a whole than C2H2 due to the additinal CH bonds.

Can you explain that a little bit. Alkanes donot readily participate in reactions, whereas alkenes and alkynes do.

 

[Charles_Carmichael]

What you also have to realize is that bond dissociation energy is determined from homolytic cleavage, not heterolytic. Homolytic cleavage means that both atoms of the bond that's been broken receive an electron each (from the bond); so, free radicals are the result. Heterolytic cleavage would result in the formation of an anion and cation because the electrons of the bond would be distributed unevenly.

An example would be HCl. It's bond dissociation energy is very high because of the vast difference in electronegativity. It's much easier for H+ and CL- (an unequal distribution of electrons from the bond) to form rather than hydrogen and chlorine free radicals.

 

[inaccensa]

What you also have to realize is that bond dissociation energy is determined from homolytic cleavage, not heterolytic. Homolytic cleavage means that both atoms of the bond that's been broken receive an electron each (from the bond); so, free radicals are the result. Heterolytic cleavage would result in the formation of an anion and cation because the electrons of the bond would be distributed unevenly.

An example would be HCl. It's bond dissociation energy is very high because of the vast difference in electronegativity. It's much easier for H+ and CL- (an unequal distribution of electrons from the bond) to form rather than hydrogen and chlorine free radicals.

So you are saying that the dissociation energy necessarily doesn't depend upon the # of bonds. It also depends on polarity. So if I compare lets say

propene and propane, the bond dissociation energy will be higher for propene, since the double bond is more stable than the propane.

However, if we to compare propylene and acetone, the dissociation energy will be more for acetone

 

[RogueUnicorn]

Can you explain that a little bit. Alkanes donot readily participate in reactions, whereas alkenes and alkynes do.

the reason is given in my previous post.

 

[inaccensa]

the reason is given in my previous post.

I'm really confused. Are we saying that an alkane is more stable or alkyne.
bonds dissociation energy (KJ/mol)
C-C 348
C=C 614

Since more energy is req to break C=C, like you said more stable bonds, more energy required to break a bond. However, you said that ethane may be more stable overall than ethylene. Hence the confusion.

 

[RogueUnicorn]

I'm really confused. Are we saying that an alkane is more stable or alkyne.
bonds dissociation energy (KJ/mol)
C-C 348
C=C 614

Since more energy is req to break C=C, like you said more stable bonds, more energy required to break a bond. However, you said that ethane may be more stable overall than ethylene. Hence the confusion.

ethane has two more C-H bonds, which will have its own bond dissociation energy to account for. remember, as an OVERALL MOLECULE, the stability will be determined by the sum of the bond enthalpies

 

[inaccensa]

ethane has two more C-H bonds, which will have its own bond dissociation energy to account for. remember, as an OVERALL MOLECULE, the stability will be determined by the sum of the bond enthalpies

So as an overall molecule, ethane is more stable than ethylene?

 

[RogueUnicorn]

So as an overall molecule, ethane is more stable than ethylene?

i actually don't recall off the top of my head, but i believe so.

 

[inaccensa]

k thanks

 

[inaccensa]

I may be getting a grip of this.

So for Ethane, there are 6 C-H and one C-C, whereas Ethylene has 4 C-H and one C=C. The C-H =413KJ/mol, C-C = 347KJ/mol, C=C 607KJ/mol
Ethane = 2825 KJ/mol
Ethylene= 2259KJ/mol

ha, so i has read that correcly, Alkanes are indeed more stable. But again to find stability, we must consider all the different bonds in the entire molecule.
Although triple bond is stronger, corresponding alkane molecules are strongest!!! I finally understand😀

 

[RogueUnicorn]

I may be getting a grip of this.

So for Ethane, there are 6 C-H and one C-C, whereas Ethylene has 4 C-H and one C=C. The C-H =413KJ/mol, C-C = 347KJ/mol, C=C 607KJ/mol
Ethane = 2825 KJ/mol
Ethylene= 2259KJ/mol

ha, so i has read that correcly, Alkanes are indeed more stable. But again to find stability, we must consider all the different bonds in the entire molecule.
Although triple bond is stronger, corresponding alkane molecules are strongest!!! I finally understand😀

yay!