What does the first law of thermodynamics state?

The first law of thermodynamics, often referred to as the law of energy conservation, states that energy cannot be created or destroyed in an isolated system. Instead, it can only be transformed from one form to another or transferred between systems. This means that the total energy of an isolated system remains constant; it may change its form, such as from kinetic energy to potential energy or from internal energy to heat energy, but the overall amount of energy will not change.

This principle is foundational in both classical mechanics and thermodynamics, influencing how we understand energy transfer processes in chemical reactions, engines, and various physical systems. The emphasis on energy conservation underpins many scientific and engineering principles, leading to a more profound understanding of both natural phenomena and the operation of various technologies.