What is the standard molar entropy of ions in solution based on the conventional scale?

The standard molar entropy of ions in solution is referenced against a particular scale, where the standard molar entropy of certain species is set to zero as a point of reference. This convention specifically applies to the hydrogen ion (H+) in aqueous solution.

Setting the standard molar entropy of H+ at zero reflects its role as a reference point for other species in thermodynamic calculations. By defining the standard molar entropy of H+ in aqueous solution as zero, we can compare the entropic values of other ions, such as Na+, Cl-, and K+, which have positive values of standard molar entropy since they possess disorder due to their existence in solution, influenced by their interactions with water molecules.

This choice highlights the importance of H+ in thermochemical studies, since it acts as a pertinent reference point in the formulation of various equations and analyses involving ionic substances in aqueous solutions. Thus, the standard molar entropy of H+ being zero is a widely accepted convention in the field of physical chemistry.