[TrueBlood]

I am doing some practice passages for the MCAT, and one of the question-sets have a table with bond energies listed.

The bond between a hydrogen and an sp2-hybridized carbon is greater than the bond energy between a hydrogen and an sp3-hybridized carbon.

Thus, it takes more energy to break the bond. But, according to the book, the more s-character in the carbon with the hydrogen... the more acidic it is. So a hydrogen attached to a sp-hybridized carbon is the most acidic, followed by an sp2-hybridized carbon and then a sp3-hybridized carbon (least acidic).

For a hydrogen to be more acidic, wouldn't it take less energy to break the bond?

[Honclbrif]

When they refer to breaking the bond, they mean homolytic cleavage: you break the bond by creating two radicals. This involves completely removing one of the electrons from the orbital in question. Since sp² has more s character than sp³, removing an electron from the sp² requires more energy.

Removing a proton is heterolytic cleavage of that bond, the electron pair remains in the sp² orbital. Since again, it is more stable than the sp³ orbital, it is more favorable to have the electrons there.