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Medical Term:

equilibrium constant


in the reaction A + B ? C + D at equilibrium (no net change in concentrations of A, B, C, or D), the concentrations of the four components are related by the equation Keq = [C][D]/[A][B]; Keq is the equilibrium constant If any component in the reaction has a multiplier (H2 ? 2H), that multiplier appears as an exponent in the calculation of K (Keq = [H]2/[H2]). When this equation is applied to the ionization of a substance in solution, Keq is called the dissociation constant (Kd) and its negative logarithm (base 10) is the pKd.

See Also: Henderson-Hasselbalch equation, mass:action ratio

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