[vitaly]

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 NH3to H2O and (k-1) - rate of exchange from H2O to NH3.

2 Question. What is the relationship between k1, k-1 and kf, kr?

[Big-Daddy]

Your question makes no sense. What do you mean "NH4+ or NH3 exchanging with H2O"? NH4+ = H2O is not an acceptable reaction equation (nor is NH3 = H2O), because atom conversion is not upheld.