Carbonyl vs. alkene bond energy

[MD2BEEE]

I'm confused as to why the C-O double bond of a carbonyl is shorter and stronger (higher bond energy) than the C-C double bond of an alkene.

Also, while we're at it... why does the pi bond of most carbonyl's have greater bond energy than the sigma bond?

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[vickpick]

its shorter because there has more overlap in the orbitals...
pi bond has greater energy *(Potential energy) because there is more repulsion between the e-'s

 

[Artful Dodger]

its shorter because there has more overlap in the orbitals...
pi bond has greater energy *(Potential energy) because there is more repulsion between the e-'s

and it's stronger because of a dipole moment. oxygen is more electronegative than carbon, so there is a stronger attraction between C and O than a C=C bond.