16.1.1—Internal energy is determined by the state of the system and that it can be

Internal energy U is the total microscopic kinetic and potential energy of a system. Its change depends only on initial and final states, not on the path.

Separate state variables from process quantities such as heat transfer and work, which depend on how the change occurs.

A gas can reach the same final temperature by slow compression or heating; its ∆U is the same if the initial and final states match.

Internal energy is not “heat contained” in an object, and work is not a state variable.