• id: JTHERM-01-N02
• title: Internal Energy of an Ideal Gas
• tags: internal-energy, state-function, temperature

Internal energy U is the sum of all microscopic kinetic and potential energies of the molecules. For an ideal gas (no intermolecular forces), U depends only on temperature: $U = nC_vT = (f/2)nRT$, where f is the degrees of freedom. This is a state function — its change $\Delta U$ depends only on initial and final states, not on the process. For real gases, U also depends on volume (due to intermolecular forces). Key: in any process, $\Delta U = nC_v\Delta T$ regardless of whether the process is at constant volume or not.