Internal energy

Internal energy is more in gases than liquids and solids. For example, when the rice is boiling in a vessel which has closed with a plate, then the plate moves, finally it falls down from the vessel to the ground because the internal energy of gases causes it falls down.
Internal energy has ingrediants of potential energy and kinetic energy.
Potential energy arises due to interaction of atoms in the molecules and also one atom with another atom
Kinetic energy arises due to translatory,rotational and vibrational motion molecules. Mainly, translatory motion of molecules occurs due to thermal energy applied on the system. So, different molecules of gas gets different energies, so that there is random motion of molecules. For that, according to classical mechanics, we can get only average translatory kinetic energy of gas molecules which is given by

At absolute temperature T=0K, the translational kinetic energy becomes zero, so that the internal energy is only due to the vibrational and rotational kinetic energies of gases. This energy is called zero point energy.
There is no change in the internal energy due to exchange of temperature with the system, but to there is change in the internal energy due to exchange of heat, because when heat is the energy quantity.
One of the important point to remember is that when external energy is applied on the system, the internal energy increases due to translational kinetic energy of molecules of the gas.