3. Internal Energy

Internal Energy Explanation

Internal energy U of a system or a body with well defined boundaries is the total of the kinetic energy due to the motion of molecules and the potential energy associated with the vibrational motion and electric energy of atoms within molecules. Internal energy also includes the energy in all the chemical bonds. From a microscopic point of view, the internal energy may be found in many different forms. For any material or repulsion between the individual molecules.

Internal energy is a state function of a system and is an extensive quantity. One can have a corresponding intensive thermodynamic property called specific internal energy, commonly symbolized by the lowercase letter u, which is internal energy per mass of the substance in question. As such the SI unit of specific internal energy would be the J/g. If the internal energy is expressed on an amount of substance basis then it could be referred to as molar internal energy and the unit would be the J/mol.

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