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How does pKa affect equilibrium?

Answer 1

Maya Allen

Consider what #"pK"_"a"# represents: the negative logarithm of the equilibrium expression for acid dissociation,

#K_"a" = ([H^+][A^-])/([HA])#

To be sure, its magnitude is inversely proportional to the amount of dissociation the acid undergoes in solution.

Consider a reaction,

We can look at this from a perspective of the magnitudes of #"pK"_"a"# values.

Alkanes: #~55#

Phenol: #~10#

The latter is far more likely to dissociate in this solution, and hence, the equilibrium will probably favor the left.

In non-scientific language (which helped me more during organic chemistry): the alkane is happy with its proton, but the phenol isn't.

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Answer 2

Addison Armstrong

pKa directly influences the equilibrium position of an acid-base reaction. A lower pKa indicates a stronger acid, favoring the dissociation of the acid and shifting the equilibrium towards the formation of more products. Conversely, a higher pKa suggests a weaker acid, leading to less dissociation and a shift in equilibrium towards fewer products.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.