What is internal energy?
In the example when you touch something hot like a stove, you might think that there is heat in the stove but heat is only the energy being transfer. The energy in the stove is called Internal Energy. It is made up of the energy of the fast moving atoms and the energy stored in the bonds that hold the atoms of the stove together. The hotter something is the more internal energy the object has. The diagram on the right shows an image of atoms held together with bonds, this is what a molecule of a solid or liquid would look like. When heat is transferred to the atoms they move very quickly, if enough heat is transferred then the bonds will break and the molecule will changestate (melt or boil).