heat of combustion

[inaccensa]

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The heat of combustion for Butane is 45.752 MJ/Kg, whereas that for isobutane is 45.613MJ/Kg. does this mean that n-butane is less stable than Isobutane?

 

[ThirdEye]

......

 

[inaccensa]

It should be more stable since it requires more energy to undergo combustion. However I could be missing something.

I was confused too. Why is isobutane more stable? I thought branching decreased the london dispersion forces. Although that is strictly for bp, but shouldn't the intermolecular forces affect combustion too

 

[thebillsfan]

I was confused too. Why is isobutane more stable? I thought branching decreased the london dispersion forces. Although that is strictly for bp, but shouldn't the intermolecular forces affect combustion too

it is more stable, i think, because of hyperconjugation. but you dont need to know that for the mcat. as you can tell, its not much more stable so they're basically the same. a lower heat of combustion means its more stable, always.

 

[pastryman]

ive heard branching increases stability

 

[ezsanche]

I was confused too. Why is isobutane more stable? I thought branching decreased the london dispersion forces. Although that is strictly for bp, but shouldn't the intermolecular forces affect combustion too

In combustion you are breaking covalent bonds and forming new ones. This involves INTRAMOLECULAR forces not intermolecular forces.

the lower the energy released during combustion= the more stable it is

 

[ThirdEye]

I had it backwards. These guys are right. Butane is less stable because less stable molecules are more combustable.