Final answer:
The standard molar entropies of ions in solution have a baseline where the entropy of the hydrated proton is zero. Entropy changes for processes are calculated using the entropies of products and reactants. For instance, the condensing of iodine gas into a solid has a negative entropy change.
Step-by-step explanation:
The standard molar entropies of ions in solution are not always negative or positive, and do not reference the entropy of water or air. They have a specific scale where the entropy of the hydrated proton (H+ ion in aqueous solution) is set to zero. This allows for the calculation of standard free energies of other ions in solution relative to this baseline.
When analyzing entropy changes in various processes, like the condensing of iodine gas into a solid or an ice cube melting, it's crucial to understand that the entropy change is equal to the sum of the standard entropies of the products minus the sum of the standard entropies of the reactants, each multiplied by their stoichiometric coefficients. For example, the condensing of iodine gas would have a negative change in entropy because the process involves a transition from a disorderly gas phase to a more orderly solid phase.