Can an acid base reaction be at equilibrium?

And how would I know?

1 Answer
Truong-Son N.
Feb 3, 2018

Always... but...

...if they are both weak acids and bases, then we actually care.

  • #"CH"_3"COOH""/NaHCO"_3# makes an equilibrium
  • #"CH"_3"CH"_2"ONa""/H"_2"O"# makes an equilibrium

etc. If one of them is strong, then who cares? The "equilibrium" would strongly favor the dissociated strong acid or base, and you basically won't even have the original acid or base in solution anymore. That leaves you with just one thing in solution, not two...

An acid-base reaction (that is, an acid+base IN water) always gets to AN equilibrium, but it won't be evenly balanced unless the relative weak acid strengths are similar. Given

#"pK"_a("CH"_3"COOH") = 4.76#
#"pK"_(a1)("H"_2"CO"_3) = 6.35#
#"pK"_a("H"_2"O") = 15.7#
#"pK"_a("CH"_3"CH"_2"OH") = 15.9#

show that the first equilibrium lies towards the right by a factor of #38.9#, and that the second equilibrium lies towards the right by a factor of #1.58#.

When an equilibrium lies to the right or left by a factor of #100+#, we stop caring and just look at the weaker acid, as we miss half the components in an acid-base equilibrium.

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