why can't you convert cis-2-butene into trans-2-butene simply by undergoing a rotation/

Question

The cis and trans isomers of 2-butene involve a pi bond as well as a sigma bond. To "rotate" the molecule, the pi bond must be broken (remember this double bond is planar) and that involves about 70 kcal of energy so a simple interconversion isn't possible; for example, at room temperature.