[paulhao]

H2NCH2CO2H  H3N⁺CH2CO2^-

How do I know which side is the favored equilibrium?

I guess it's the left because it's more stable?

[pgk]

In your opinion, which one is more stable; a mixture of an acid and a base or their salt?

[spirochete]

For some examples in acid base chemistry I wonder if it's possible to predict based on first principles. For example here there is the destabilizing effect of charge weighing against resonance stabilization and maybe differing bond strengths.

Long story short I think the best way to do it is to just look up the pKa's for the acids on either side of the equation. One  reasonable approximation would be comparing the pKa for acetic acid with the pKa for a protonated amine. Of course the pKa's for the real amino acid would be even better.

Guesses based on qualitative factors might be incorrect if you're comparing apples to oranges.

[Babcock_Hall]

Are we talking about an aqueous solution or a non-aqueous solution?  I will assume the former, unless I am told otherwise.  Have you been given the pK_a values for each site?  If so, how could you use those values?

[paulhao]

well, we can look at the table and figure out easily.But does anyone know how to predict ?

[Babcock_Hall]

@OP,

Do you think that your original prediction was correct?  If not, what did you learn?