$$ \ce{CaCl2(s)-> Ca^{2+}(aq) + 2Cl-(aq)} $$

For the process of solid calcium chloride dissolving in water, represented above, the entropy change might be expected to be positive. However, \(\Delta S\) for the process is actually negative. Which of the following best helps to account for the net loss of entropy?

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A decrease in entropy means going from a disordered system into a more ordered system. Going through the answer choices:

The size of the ions is not relevant, especially since only the product species are being compared.

Particles are ordered more in solids than amorphous solids, but this explanation is not related to our question.

Water molecules that form the hydration shell may be inhibited from moving, therefore reducing random motion. This could affect the level of order since the ion-hydration shell complex behaves like an ordered solid that is restricted from moving.

If the calcium and chlorine ions were free to move around, this explanation would require the entropy to increase since the system is more disordered. The third choice proposes a mechanism where the ions are not exactly free to move around.