Cis-trans isomers internal energy Whilst reading about stereochemistry, I came to know that the stability and melting point of cis isomers is lower than trans isomers. By searching on net I've found the reason behind that. But one question arises - why is the internal energy of cis isomers bigger than of trans isomers?
I can think of two reasons:
1) Steric repulsion
2) Electrostatic interaction

Steric repulsion: cis means in same side. So, sterically it is suitable to be on opposite side. It is a fundamental nature of both human and chemical entity to define a personal boundary (My personal opinion :) )
In the image you can see the personal boundary of $\ce{-CH_3}$ is the furthest in the trans configuration and that's wh the trans configuration is more stable than the cis configuration.

Electrostatic interaction: Due to electrostatic interaction, molecules or functional group try to distance themselve as far as possible. This also results in lower energy in trans configuration.