What is the difference between dissociation constant and equilibrium constant

Notice the inverse relationship between the strength of the parent acid and the strength of the conjugate base. Thus the conjugate base of a strong acid is a very weak base, and the conjugate base of a very weak acid is a strong base. We can use the relative strengths of acids and bases to predict the direction of an acid—base reaction by following a single rule: an acid—base equilibrium always favors the side with the weaker acid and base, as indicated by these arrows:.

In an acid—base reaction, the proton always reacts with the stronger base. Hence the ionization equilibrium lies virtually all the way to the right, as represented by a single arrow:. In contrast, acetic acid is a weak acid, and water is a weak base. Similarly, in the reaction of ammonia with water, the hydroxide ion is a strong base, and ammonia is a weak base, whereas the ammonium ion is a stronger acid than water. Hence this equilibrium also lies to the left:. All acid—base equilibria favor the side with the weaker acid and base.

Thus the proton is bound to the stronger base. Recall from Chapter 4 that the acidic proton in virtually all oxoacids is bonded to one of the oxygen atoms of the oxoanion.

Conversely, the conjugate bases of these strong acids are weaker bases than water. How can this be true? The equilibrium constant I have calculate is about times larger than the acid dissociation constant! An acid dissociation constant is a particular example of an equilibrium constant.

They're not exactly the same. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Learn more. Acid dissociation constant and equilibrium constant Ask Question. Asked 6 years, 10 months ago. Active 3 years, 7 months ago. A moment of silence for nomenclature. Who decided we were going to call things k something , and why? The exact origins of "k" are lost in antiquity, and one can only assume that "k" stands for konstant , from German.

By agreed-upon convention of pharmacology , lower case "k" is used to denote rate constants such as k on and k off , whereas uppercase K is used for equilibrium constants such as K d. The "on" and "off" terminology has been retained here because it is used by the college examiners in Question 12 from the second paper of Units for k on are units of [D] multiplied by the units of [R] over time, i. Units for k off are units of [DR] over time.

K d is the dissociation constant. K a is the association constant. It is the opposite of K d ; i. The colloquial term "affinity" is often used interchangeably with K a ; however affinity as a chemical definition is actually something slightly different. Affinity is usually used to describe how avidly a drug binds to its receptor.

This concept is borrowed from chemical physics and physical chemistry, where affinity is defined as the quantifiable representation of the tendency of dissimilar chemical species to form chemical compounds.