The First Law of Thermodynamics is also called the Law of Conservation of Energy. It states that energy cannot be created or destroyed; it can only change from one form to another. In other words, the total amount of energy in an isolated system always remains constant, though it may appear in different forms such as heat, work, or internal energy.
For example:
- When fuel burns in an engine, the chemical energy is converted into heat and then into mechanical work.
- In a steam turbine, heat energy of steam is converted into kinetic energy that produces electricity.
Mathematically, it is often expressed as:
Change in Internal Energy (ΔU) = Heat Added to the System (Q) – Work Done by the System (W)
This law is important because it explains how energy flows in physical, chemical, and biological processes. It ensures that in every process, the energy lost from one form is exactly equal to the energy gained in another form.