Internal Energy
The total microscopic energy contained within a thermodynamic system, comprising kinetic energies of particle translational/rotational/vibrational motion and potential energies of intermolecular forces.
Governing formula
U = (f/2) n R T (for ideal gas)
SI unit
J
In depth
Internal energy is a state function depending only on current state variables (T, P, V), not path. For a monoatomic ideal gas, U depends strictly on temperature T.
Examples in the real world
Heating 1 mole of helium gas increasing its internal energy by 12.47 Joules for every 1 Kelvin rise in temperature.