While a carbon-carbon double bond is stronger than a single bond, it is not twice as strong. The strength of a chemical bond is determined by several factors, including the number of electrons shared between the atoms, the electronegativity of the atoms, and the bond length.

In the case of a carbon-carbon double bond, there are two pairs of electrons shared between the carbon atoms. This is more than the single pair of electrons shared in a single bond, but it is not double the number. Additionally, the electronegativity of carbon is relatively low, which means that the electrons are not held very strongly by either atom. Finally, the bond length of a double bond is shorter than that of a single bond, which means that the electrons are held more closely together.

All of these factors contribute to the fact that a carbon-carbon double bond is not twice as strong as a single bond. In reality, it is only about 1.5 times stronger.