The logarithm (to the base 10) of the reciprocal of the equilibrium constant for a specified reaction under specified conditions (for example, solvent and temperature). pK values are often more convenient to tabulate and use than the equilibrium constants themselves. The value of K for the dissociation of the HSO₄^- ion in aqueous solution at 77°F (25°C) is 0.0102 mole/liter. The logarithm is 0. 008₆ − 2 = −1.991₄. pK is therefore +1.991₄. The choice of algebraic sign, although arbitrary, results in positive values for most dissociation constants applicable to aqueous solutions. The concept of pK is especially valuable in the study of solutions.