The first law of thermodynamics is a fundamental principle in thermodynamics that states that energy cannot be created or destroyed, but it can be transformed from one form to another. This law is also known as the law of conservation of energy.

The first law of thermodynamics can be expressed mathematically as follows:

ΔU = Q – W or Q = ΔU + W

where ΔU is the change in internal energy of a system, Q is the amount of heat added to the system, and W is the work done on the system.

This equation means that any change in the internal energy of a system can only occur if energy is either added or removed from the system in the form of heat or work. In other words, the total energy in a system is always conserved.

One way to understand this law is to think of a simple example, such as a pot of boiling water on a stove. Heat is added to the pot, which causes the water molecules to move faster and faster until they reach a boiling point. The internal energy of the water has increased due to the heat added to the system.

The first law of thermodynamics is closely related to the concept of entropy. Entropy is a measure of the disorder or randomness of a system. The second law of thermodynamics states that the total entropy of a closed system always increases over time.

This means that, even though the total energy in a system is conserved, the energy tends to disperse and become less useful over time. For example, in the case of the boiling pot of water, heat energy flows from the stove to the water, increasing the entropy of the system. As the water cools, the heat energy disperses into the environment, increasing the overall entropy of the universe.

The first law of thermodynamics is a powerful tool for understanding many natural processes, from the behavior of stars to the workings of the human body. It is used in many fields, including chemistry, physics, and engineering.

In summary, the first law of thermodynamics states that energy is always conserved, and can neither be created nor destroyed. It can only be transformed from one form to another, and any change in the internal energy of a system is caused by the addition or removal of energy in the form of heat or work. The first law of thermodynamics is a fundamental principle in science and has important implications for understanding many natural processes.