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An ion-dipole attraction couples an ion's electric field to a molecule's electric dipole moment. In the elementary point-electric dipole approximation, the interaction potential energy is $U=-\mathbf{p}\cdot \mathbf{E}$. An orientation with the electric dipole moment along the electric field lowers this energy. For water, the oxygen end preferentially faces a cation, and the hydrogen end an anion. At nonzero temperature, fluctuations and competing hydrogen bonds prevent perfect alignment of every molecule.^[ref]

Solvent-specific stabilization means that the same species need not have the same solvation free energy in different solvents. Chemical polarity, hydrogen bonds, and the cost of reorganizing each solvent all matter. Water can stabilize ions by ion-dipole attractions; a favorable isolated attraction alone still cannot decide the total dissolution balance.^[ref]

With a common gaseous reference and compatible dissolved standard states, subtraction removes that reference:A negative result favors solvent B under those reference conventions. This comparison assumes the same species $X$: if protonation, ionization, or formation of ion pairs changes its identity, include a chemical equilibrium for each corresponding chemical reaction.