positional (residual) entropy

[Adrienne_4F]

How does positional (residual) entropy differ from normal entropy?

[Christopher Tran 1J]

Normal entropy refers to the randomness exhibited by the elements of a system due to their constant movement (like molecules in liquid).

Residual entropy is entropy at absolute zero, meaning that the elements are no longer moving. Even though there is no movement, there is still residual entropy due to the fact that there is disorder in the positions of the elements within the system. The number of possible combinations of positions for the elements determine the residual entropy.

[Nina Do 4L]

Residual entropy is like a screenshot of the molecules in stationary form but we need to also calculate entropy for its other possible orientations since some molecules can have resonance such as COF2 and BF3. They are both trigonal planar but BF3 is non polar and doesn't have resonance; the three florins have to be around the Boron. But COF2 has different orientations so that is when you would use positional entropy.