Internal energy
The internal energy of a system (abbreviated E or U) is the total kinetic energy due to the motion of molecules, and the total potential energy associated with the rotational, vibrational, and electric energy of atoms within molecules. Internal energy is a quantifiable state function of a system.
For systems consisting of molecules, the internal energy is partitioned among all of these types of motion. In systems consisting of monatomic particles, such as helium gas and other noble gasses, the internal energy consists only of the kinetic energy of the individual atoms. Monatomic particles, of course, do not rotate or vibrate, and are not excited to higher electrical energies, except at very high temperatures.
Each molecular energy state has its own internal energy.
Measurement
Internal energy can not be measured directly; it is only measured as a change (ΔU). The equation for change in internal energy is:
- <math>\Delta U = q + w \,\!<math>
- q is heat. When heat transfers energy from the system to the surroundings, the symbol is -q. When heat transfers energy from the surroundings to the system, the symbol is +q.
- w is work. When work transfers energy from the system to the surroundings, the symbol is -w. When work transfers energy from the surroundings to the system, the symbol is +w.
See also
I think the work signs are reversed. System to surrounding is POSITIVE work and surrounding to system is NEGATIVE
