What is a system which one of the equation is for the first law of thermodynamics?

The first law of thermodynamics, which states that energy cannot be created or destroyed, only transformed, can be represented in a closed system where energy exchange occurs. The equation often used is ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system. This law applies to various systems, including engines, refrigerators, and biological systems, illustrating how energy is conserved and transferred.