# don't understand what is exchanging with what in this acid/base equilibrium

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Thread starter 6 years ago
#1
NH4+ + H2O (kr) = (kf) NH3 + H3O+;

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

I assume that at pH=7, the likely case is:
NH4+ + H2O (kr) = (kf) NH3 + H3O+

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

1 Question. NH4+ or NH3 is exchanging H+ with H2O?

If NH4+ is exchanging H+ with H2O:
NH4+ (k-1) =(k1) H2O, transfer of H+ between them.

where (k1) - pseudo first order rate constant of H+ transfer from NH4+ to H2O and (k-1) - pseudo first order rate constant of H+ transfer from H2O to NH4+.

If NH3 is exchanging H+ with H2O:
NH3(k-1) =(k1) H2O, transfer of H+ between them.

where (k1) - pseudo first order rate constant of H+ transfer from NH3to H2O and (k-1) - pseudo first order rate constant of H+ transfer from H2O to NH3 .

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

Depending on the answer to 1st question, I would like to get something like this: k1=kr*[NH3 ]
0
6 years ago
#2
(Original post by alex_alex)
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?
Your notation is all wrong. This may be because of having to type it or maybe because you have it wrong.

kn (n can be anything) is the rate constant for the forward reaction, e.g. NH3 + H3O+ -> NH4+ + H2O
k(-n) is the rate constant of the reverse process. NH4+ + H2O -> ......

K is the overall equilibrium constant, note that the rate constant isn't capitalised. How you have put the rate constants in (i.e. in with one side of the reaction) makes no sense. It isn't possible to put down the proper notation in this format, you have to write it really, but it is....
You have the kn and k(-n) notations above and below the equilibrium sign matching with which wa the arrows point in the eq symbol. This should mean kn is above.
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Thread starter 6 years ago
#3
(Original post by JMaydom)
Your notation is all wrong. This may be because of having to type it or maybe because you have it wrong.

kn (n can be anything) is the rate constant for the forward reaction, e.g. NH3 + H3O+ -> NH4+ + H2O
k(-n) is the rate constant of the reverse process. NH4+ + H2O -> ......

K is the overall equilibrium constant, note that the rate constant isn't capitalised. How you have put the rate constants in (i.e. in with one side of the reaction) makes no sense. It isn't possible to put down the proper notation in this format, you have to write it really, but it is....
You have the kn and k(-n) notations above and below the equilibrium sign matching with which wa the arrows point in the eq symbol. This should mean kn is above.

Please, do not change the reaction direction, because originally:
NH4Cl = NH4+ + Cl-.

The notation I used to differentiate between reaction rate constant (kf, kr) and H+ exchange rate constant (k1, k-1). I am trying to establish a relationship between them. I am not sure I understand NH4+ or NH3 is exchanging H+ with H2O?

At pH=7, I assume that 1st one is the most likely case. NH4+ + H2O (kr) = (kf) NH3 + H3O+;
0
6 years ago
#4
(Original post by alex_alex)
Please, do not change the reaction direction, because originally:
NH4Cl = NH4+ + Cl-.

The notation I used to differentiate between reaction rate constant (kf, kr) and H+ exchange rate constant (k1, k-1). I am trying to establish a relationship between them. I am not sure I understand NH4+ or NH3 is exchanging H+ with H2O?

At pH=7, I assume that 1st one is the most likely case. NH4+ + H2O (kr) = (kf) NH3 + H3O+;
It doesn't matter which direction you put the reaction. If anything I have put it the right way as the hydronium is way more acidic than ammonium and placing this on the right implies the opposite (but only implies, doesn't actually mean it is)

Please actually define what you mean by NH3 exchanging with H2O etc. This doesn't mean anything specific. I could guess but I'm not going to potentially waste our time when you could write it out properly.
(NH3 = H2O is not an acceptable equation to write... write out fully what you mean)
Also you probably need the relation K=kn/k(-n) to answer some of your questions.
0
Thread starter 6 years ago
#5
(Original post by JMaydom)
It doesn't matter which direction you put the reaction. If anything I have put it the right way as the hydronium is way more acidic than ammonium and placing this on the right implies the opposite (but only implies, doesn't actually mean it is)

Please actually define what you mean by NH3 exchanging with H2O etc. This doesn't mean anything specific. I could guess but I'm not going to potentially waste our time when you could write it out properly.
(NH3 = H2O is not an acceptable equation to write... write out fully what you mean)
Also you probably need the relation K=kn/k(-n) to answer some of your questions.
I tried to detail the question as much as I could. Please, reread the original question description. I hope it is now clear I am trying to do. Please, let me know if I still did not manage to clarify something. Thank you for your time.
0
6 years ago
#6
(Original post by alex_alex)
I tried to detail the question as much as I could. Please, reread the original question description. I hope it is now clear I am trying to do. Please, let me know if I still did not manage to clarify something. Thank you for your time.
Well be that way... You have your equations wrong and I'm offering to help.
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