Why do some molecules have more energy than others?

Every molecule is composed of individual atoms that are attached to each other through bonds that contain energy. These bonds may be strong or weak. The strongest bonds contain the most energy while the weakest bonds have the least energy.  

The amount of energy that a molecule has depends on the types of chemical bonds that hold its constituent atoms. Stronger bonds, such as covalent bonds, require more energy to break, while weaker bonds, like hydrogen bonds, have lower energy requirements.