The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed between forms (kinetic, potential, heat, and other internal forms), and this principle underlies the definition of internal energy (U) — the total energy contained within a system, including kinetic, potential, rotational, vibrational, bond, and electrical potential energy of its constituent particles. The change in a system's internal energy (ΔU) is formally related to heat transfer and work via ΔU = Q − W (heat added minus work done by the system), an equation belonging to the domain of thermodynamics within physics and chemistry. This concept connects macrostate descriptions like temperature and heat to microstate descriptions of particle motion, and simplifies for an ideal monoatomic gas to purely kinetic energy.
The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed between forms (kinetic, potential, heat, and other internal forms), and this principle underlies th…