Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Keq Concept: No Liquids in Keq

  1. Nov 10, 2011 #1
    So I see in my book that for an acid dissociation, the Ka = K eq [H 2 O]
    and that the Keq includes H2O in the eqn. Shouldn't there be no liquids in Keq?

    Keq = [H 3 O + ] [A - ]
    [HA] [H 2 O]

    Why is there H2O in Keq?
    If I am asked to calculate Keq do I have I have to include [H2O]?

    Thanks
    _______________
     
  2. jcsd
  3. Nov 11, 2011 #2

    DrDu

    User Avatar
    Science Advisor

    That's a question of standard state. For diluted substances you use, simplified, the concentration c divided by the concentration [itex] c^0[/itex] =1 mole/l, e.g. [itex] [HA]=c_{HA}/c^0_{HA} [/itex]. For the solvent you use as standard state the pure solvent that is for water [itex] c^0=[/itex] 55.5 mole/l.
    So the concentration of H2O in a dilute solution of the acid is very nearly the concentration of H2O in pure water, hence the quotient which enters the equilibrium factor is nearly 1.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Keq Concept: No Liquids in Keq
  1. Diamagnetic liquid (Replies: 1)

  2. Liquid CO₂ (Replies: 2)

Loading...