What is internal energy?

Internal energy is the total energy contained within a system, encompassing both kinetic and potential energy at the molecular level. It reflects the energy associated with the random motion of particles and the interactions between them. Changes in internal energy can occur due to heat transfer or work done on or by the system.

The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another. This principle implies that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system. It establishes a fundamental relationship between heat, work, and internal energy.

State functions are properties that depend only on the current state of a system, not on the path taken to reach that state. Internal energy is a state function, meaning its value is determined solely by the system's current conditions, such as temperature and pressure, rather than how the system arrived at those conditions. This characteristic is crucial for understanding thermodynamic processes.