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It is really hard to determine the entropy change of a reaction accurately because of subtle solvent effects and a lack of standard entropies. On the other hand, enthalpy is relatively easy and through a thermodynamic cycle, it can usually be calculated. But what about our knowledge of entropy limits our ability to measure it? Without using straight empirical data, why is using force field and electronic interactions not very reliable? Many reactions face this problem, like the mixing of liquids.

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    $\begingroup$ Generally speaking, what you say is not true, tables of standard entropy (and enthalpy ) can be found easily, such as in the data section of Atkins' phys chem textbook. Any problems of accuracy will exist for both entropy and enthalpy. $\endgroup$ – porphyrin Jun 26 at 12:10
  • $\begingroup$ Since G = H-TS, any inaccuracies in H or S reflect on each other directly. $\endgroup$ – Jon Custer Jun 26 at 16:15
  • $\begingroup$ Porphyrin, that is simply not true when it comes to solvent effects. You can't just use standard entropies when you are trying to solve for the solvation entropy change. Also there are many compounds that do not have standard entropies in tables when it comes to acids and bases. $\endgroup$ – Nathan Matthieu Tang Jul 10 at 2:25

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