For a closed system the internal energy is essentially defined by
ΔU = q + W
- U is the change in internal energy of a system during a process
- q is the heat
- W is the mechanical work.
If an energy exchange occurs because of temperature difference between a system and its surroundings, this energy appears as heat otherwise it appears as work. When a force acts on a system through a distance the energy is transferred as work. The above equation shows that energy is conserved.
The different components of internal energy of a system is given below.
|Thermal energy||Sensible heat||Energy change of a system associated with:Molecular translation, rotation, vibration.Electron translation and spin.Nuclear spin of molecules.|
|Latent heat||Energy required or released for phase change, change from liquid to vapour phase requires heat of vaporization.|
|Chemical energy||Energy associated with the chemical bonds in a molecule.|
|Nuclear energy||The large amount of energy associated with the bonds within the nucleus of the atom.|
The physical and chemical processes that can change the internal energy of a system is given below.
|Transferring energy across the system boundary by||Heat transfer||Energy transfer from a high temperature to low temperature state.|
|Work transfer||Energy transfer driven by changes in macroscopic physical properties of a system such as compression or expansion work.|
|Mass transfer||Energy transfer by mass flowing across a system boundary.|
|Change through internal processes||Mixing||Heat releases upon components mixing that may lead to lower internal energy.|
|Chemical reaction||Heat required or released during a chemical reaction that changes chemical energy.|
|Nuclear reaction||Heat released during a nuclear reaction that changes nuclear energy.|