Physical Chemistry Chapter 2 Interna l Energy Internal energy: Total amount of energy in a system. The sum total of all kinetic and potential energy within the system Internal energy changes: The sign of AU Negative values: a system loses energy to the surroundings Positive values: a system gains energy from the surroundings6 Internal energy: Total amount of energy in a system. The sum total of all kinetic and potential energy within the system. Internal energy changes: The sign of U Negative values: a system loses energy to the surroundings Positive values: a system gains energy from the surroundings Physical Chemistry Chapter 2 Internal Energy