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

Don't understand what is exchanging with what in this acid/base equili

  1. Apr 8, 2014 #1
    NH4+ + H2O (kr) = (kf) NH3 + H3O+;

    the same reaction can be written as:
    NH4+ + HO- (kr) = (kf) NH3 + H2O;

    where (kf) - rate of forward reaction and (kr) - rate of reverse reaction.

    1 Question. NH4+ or NH3 exchanging with H2O?

    If NH4+ is exchanging with H2O:
    NH4+ (k-1) =(k1) H2O,

    where (k1) - rate of exchange from NH4+ to H2O and (k-1) - rate of exchange from H2O to NH4+.


    If NH3is exchanging with H2O:
    NH3(k-1) =(k1) H2O,

    where (k1) - rate of exchange from NH3 to H2O and (k-1) - rate of exchange from H2O to NH3.

    2 Question. What is the relationship between k1, k-1 and kf, kr?
     
  2. jcsd
  3. Apr 8, 2014 #2

    Borek

    User Avatar

    Staff: Mentor

    I don't see why you assume it is the same reaction with the same rate constants. They are definitely related to the same equilibrium, but that's all.
     
  4. Apr 8, 2014 #3
    At pH=7, I assume that 1st one is the most likely case. I am not sure I understand NH4+ or NH3 is exchanging H+ with H2O?
     
  5. Apr 8, 2014 #4

    Borek

    User Avatar

    Staff: Mentor

    To be honest, I have no idea what the exact mechanism is - at the same time I don't think it matters. Equilibrium doesn't depend on these details, and it is equilibrium that we are typically interested in.

    Please note there is no such thing as H+ nor OH- in the solution. H3O+ is only an approximation, as proton is most likely solvated by more than one water molecule. OH- is solvated as well, so it is present as - at least - H3O2-. We ignore all these and it doesn't interfere with our understanding of acid/base reactions, why should it matter for ammonia?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Don't understand what is exchanging with what in this acid/base equili
Loading...