Entropie en de tweede wet van de thermodynamica

The second law of thermodynamics can be stated via the physical quantity, entropy. It states that in any irreversible process, the universe becomes more disordered.

Consider an ideal gas of 'n' moles undergoing an adiabatic free expansion, which is an irreversible process. Since entropy is a state function, its change during this process can be calculated by considering a reversible process with the same initial and final states.

This reversible process can be approximated to an isothermal expansion.

The total entropy change is found to depend on the ratio of the volumes of the gas before and after the expansion. Here, 'n' is the amount of gas and R, the gas constant.

As the environment exchanges no heat with the gas, its entropy remains constant. Hence, the universe's total entropy has increased.

The condition of each gas molecule, described by its position and velocity, makes up the microstate.

A larger volume of the gas implies more possibilities of these coordinates for each molecule, hence, a more disordered system. Thus, entropy quantifies disorder.