What does internal energy measure?

Internal energy is a thermodynamic property that measures the total energy contained within a system due to the random motions and interactions of its molecules and atoms. This energy encompasses not only the kinetic energy associated with the motion of particles, such as translation, rotation, and vibration, but also includes potential energy from intermolecular forces.

When considering the concept of internal energy, it is critical to understand that it reflects the microscopic energy states of a system. The movement of atoms and molecules contributes significantly to the internal energy, as temperature—a measure of the average kinetic energy of particles—directly correlates with it. This relationship is foundational in thermodynamics, as it allows for the examination of energy changes within a system during various processes, such as heating, cooling, or phase changes.

The other options discuss different forms of energy but do not correctly define internal energy. For example, potential energy stored in a system refers specifically to energy due to the position or configuration of an object within a field, and while it is part of internal energy, it is not the complete definition. The total energy from nuclear reactions pertains to energy transformations occurring during nuclear interactions, which is not directly encompassed within the concept of internal energy. Lastly, the energy associated with external work done involves energy