The relationship between entropy and the first law of thermodynamics is closely linked and can be summarized by the second law of thermodynamics, which states that the total entropy of an isolated system tends to increase over time.
The first law of thermodynamics, also known as the law of energy conservation, states that energy can neither be created nor destroyed in an isolated system. It can only be transferred or transformed from one form to another. This law is often expressed in the equation:
ΔU = Q - W
Where: ΔU is the change in internal energy of the system, Q is the heat added to the system, W is the work done by the system.
Entropy, on the other hand, is a measure of the disorder or randomness of a system. It is a thermodynamic quantity that accounts for the number of possible microstates (arrangements of particles) of a system that corresponds to a given macrostate (macroscopic variables like temperature, pressure, and volume). Entropy is denoted by the symbol S.
The second law of thermodynamics introduces the concept of entropy and states that the total entropy of an isolated system tends to increase or remain constant over time. In other words, in natural processes, systems tend to evolve towards states of higher entropy or greater disorder.
The first law of thermodynamics does not directly incorporate entropy. However, when combined with the second law, the first law helps explain the direction and limitations of energy transfers and transformations. The second law indicates that some of the energy transferred or transformed within a system is dissipated as waste heat, increasing the entropy of the system and its surroundings. Thus, while the first law of thermodynamics ensures energy conservation, the second law introduces the concept of entropy to describe the irreversibility and natural tendencies of physical processes.