Entropy vs. Positional (Residual) Entropy Uses

[Jessica Lee 3D]

Hello! I understand the differences between simple entropy and positional/residual entropy, but in what situation would we use or calculate residual entropy over just entropy? How does this info help us understand more about the reaction from a practical and applicational standpoint in research per say... I guess I am just looking for ways to relate these to non-textbook related scenarios in order to help me better grasp the two concepts.

[hiranya sundar 2D]

I think for most scenarios you would be given the entropy because there are too many positions/things to account for. Positional entropy is what the entropy would be if we freeze a mole of atoms and count how many different ways they could be arranged. It isn't really applicable in real life, especially within the human body, but I think it's a nice way to understand the theory behind how entropy works and how to calculate one aspect of it.

[Anjana Shriram 2A]

Positional entropy is relevant when we cool a sample to such a low temperature (extremely close to 0K) that thermal entropy becomes insignificant.

I think Dr. Lavelle introduced positional entropy to emphasize that just because there isn't entropy due to thermal motion does not mean there is no entropy at all. As long as degeneracy (W) > 1, there will still be entropy in the system.