What does 'ΔU = q + w' represent in thermodynamics?

The equation ΔU = q + w represents the First Law of Thermodynamics, which states that the change in internal energy (ΔU) of a system is equal to the heat added to the system (q) plus the work done on the system (w). This fundamental principle establishes that energy cannot be created or destroyed, only converted from one form to another.

In this context, q represents the energy transfer due to heat, which can change the internal energy of a system, while w represents the energy transfer due to work, which also contributes to changes in internal energy. This relationship forms the foundation for understanding energy conservation in thermodynamic processes and is essential for analyzing various thermodynamic systems.

Other concepts, such as entropy, heat capacity, or heat of reaction, are related to thermodynamics but do not describe the energy relationships captured by this formula. Heat capacity refers to how much heat a substance can store per degree of temperature change, while the heat of reaction pertains to the enthalpy change during a chemical reaction. Entropy is a measure of disorder in a system and does not directly correlate to the energy conservation expressed in this equation. Therefore, the correct identification of ΔU = q + w as the First Law of Thermodynamics illustrates