CBSE Class 11-science Answered

Internal energy (E or U) is one of the thermodynamic properties of a system which is the sum of the kinetic and potential energies of the particles that form the system. Unless change takes place, we usually have no way of evaluating it. A change in internal energy (dE) is due to the transfer of energy into or out of a system, but the volume stays constant. For example, energy transferred into the system, usually heat (q) and work (w), represents an increase of internal energy (dE) of the system. Thus,

dE = q + w