Internal energy of a system

If we consider a thermodynamic system, it must contain some matter and energy. There may have different energy concerning. These energy is the sum of kinetic energy of the molecules, rotational energy, vibrational energies and other concerned energy. Exactly to say internal energy of a system is the total energy of the system. Internal energy of a system can be expressed as the state function. The reason of calling internal energy as the state function is that it is determined by the state of a system. But it is independent of the paths of obtaining. For example, temperature, volume and pressure these are internal energy. These energy is determined by the state of the system, but not with the path. Let you are heating 0 degree Celsius of water. Once the temperature of water reaches to 1000 degree Celsius. The changed energy is calculated. It is 1.8 Kcal. In every experiment you will find same result. If you do experiment by electrically or physically heating or in any other way.