What does the first law of thermodynamics state?

The first law of thermodynamics, often referred to as the law of energy conservation, fundamentally states that energy cannot be created or destroyed; it can only be transformed from one form to another or transferred between systems. This principle indicates that the total amount of energy in a closed system remains constant over time, even as it changes forms—such as from potential energy to kinetic energy or thermal energy.

This law underpins many physical processes and energy systems, ensuring that any energy input into a system must equal the energy change within that system plus any energy expelled to the surroundings. Understanding this concept is vital for fields ranging from mechanical engineering to environmental science since it helps in analyzing energy efficiency and resource management.

The incorrect choices contrast with this law: the idea that energy can be created or destroyed conflicts with the established understanding of conservation principles. Statements that suggest energy is independent of matter or that energy transfers are always 100% efficient don’t adhere to the laws of conservation and thermodynamic efficiencies, where some energy is inevitably lost as heat in actual processes. Thus, the assertion that energy cannot be created or destroyed remains the cornerstone of the first law of thermodynamics.