| Definition: | state quantity equal to the difference between the total energy of a system and the sum of the macroscopic kinetic and potential energies of the system NOTE 1 Internal energy may be expressed as a function of the state quantities of the system such as temperature, pressure, volume, masses, or amounts of substance. NOTE 2 For a closed thermodynamic system, ΔU = Q + W, where Q is amount of heat transferred to the system and W is work done on the system provided that no chemical reactions occur. NOTE 3 Specific internal energy, or internal energy per mass, is denoted u.
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