Thermodynamics is the branch of physics that deals with the relationships between heat and other forms of energy. Thermal energy is the energy a substance or system has due to its temperature, i.e., the energy of moving or vibrating molecules, according to the Energy Education website of the Texas Education Agency

The first law of thermodynamics, also known as the law of energy conservation, is a fundamental principle in the field of thermodynamics. It states that energy cannot be created or destroyed in an isolated system, but it can be transferred from one form to another or converted into different forms.

Understanding the First Law of Thermodynamics:

The first law of thermodynamics is based on the principle of conservation of energy, which states that the total energy of a closed system remains constant. This law applies to all types of energy, including heat, work, and potential and kinetic energy.

Key Points:
1. Energy Conservation: The first law of thermodynamics states that the total energy of an isolated system remains constant. In other words, the energy of a system can neither be created nor destroyed; it can only be converted from one form to another.

2. Heat and Work: The first law also relates to the transfer of energy in the form of heat and work. Heat is the transfer of thermal energy between two bodies at different temperatures, while work is the transfer of energy due to a force acting over a distance.

3. Internal Energy: The first law of thermodynamics can be expressed mathematically as ΔU = Q - W, where ΔU is the change in internal energy of the system, Q is the heat added to the system, and W is the work done by the system.

4. Sign Conventions: The sign conventions for heat and work depend on the perspective of the system. Heat added to the system and work done by the system are considered positive, while heat lost by the system and work done on the system are considered negative.

5. Energy Transfer: The first law of thermodynamics allows us to understand how energy is transferred and transformed within a system. For example, when a gas is compressed, work is done on the system, increasing its internal energy. Conversely, when a gas expands, it does work on the surroundings, decreasing its internal energy.

Conclusion:

The first law of thermodynamics is a fundamental principle that governs the conservation of energy in a closed system. It states that energy cannot be created or destroyed, but it can be transferred or converted into different forms. This law provides a foundation for understanding the behavior of energy in various thermodynamic processes and systems.