Absolute entropieën en de derde wet van de thermodynamica

Entropy is unique among state functions because it possesses a measurable, absolute value.

We define this value through the Boltzmann relationship: the absolute entropy is proportional to the natural logarithm of the number of possible microstates, or particle arrangements.

When a gas-filled container expands, a larger volume allows for more closely spaced energy levels, which become populated even at the same temperature. This increases the total number of accessible microstates, increasing the system’s entropy.

At absolute zero, all thermal motion ceases. In a perfectly ordered crystal, the atoms align in a singular, unique arrangement. Because there is only one possible microstate, the natural log of one is zero, resulting in zero entropy. This is the Third Law of Thermodynamics.

However, the "perfect crystal" is an ideal. In reality, residual entropy may persist even at zero kelvin. This occurs when molecules can be "frozen" in different orientations, like carbon monoxide molecules facing random directions. This persistent disorder means the entropy remains slightly above zero.