equilibrium constants [ENDORSED]

[Libby Stafford 1L]

Why do we not have an equilibrium constant for strong acids?

[Chem_Mod]

We do not have equilibrium constants for strong acids because strong acids are assumed to have dissociated completely.

[Christine Lin 1H]

Hi Libby,

Like the Chem_Mod said, strong acids will completely dissociate and thus we do not need to use equilibrium constants.

For example if we are given 0.01 moles of HCl (strong acid), we would assume that the HCl will completely dissociate to H+ and Cl- and that we'd also have 0.01 moles of H+.

Hope this helped :)

[KyleNagasawaDisc3C_Chem 14B2022W_]

Hey Libby,

The concept of strong acid equilibrium values is actually really interesting. In scientific literature, you actually will find instances where they define the equilibrium constants for strong acids depending on the solvent--solvents stabilize conjugate bases to different degrees. I believe the professor explained that he will not provide Ka values due to the values being so large that full dissociation is a much better approximation of the acid's dissociation behavior.

In terms of assigning Ka values to strong acids, numerous chemists use this as a means of helping to determine reactions between acids. In fact, in instances where two acid species are present in an inert solvent, the weaker acid will deprotonate the stronger acid. A classical example of this is the reaction between sulfuric and nitric acid, where nitric acid will abstract a proton from sulfuric acid and form a complex that degrades. The actual equilibrium explanation of this phenomenon will be reliant on rationalizing the differential Kas.

Remember, is it easy to make the assumption that species always act as "Acids" or always "Bases" due to the misleading nature of the pH scale. In actuality, these terms define relations between other species. In typical general chemistry courses, "strong" and "weak" acids and bases are based on relative to water.

[Hailey Sarmiento 3E]

there are no equilibrium constants for reactions with strong acids because the reaction heavily favors the forward reaction or the formation of the products since the strong acid will be completely deprotonated in solution. the equation is therefore written with only a forward arrow