Acid-base reaction:

CH3COOH  +  H2O  <===>  CH3COO-  +  H3O+
___acid__________________conjugate base_______

I found 2 explanations about the shift of equilibrium.

1.
The pKa value of hydronium ion (H3O+) is -1.7, while acetic acid is 4.7.
H3O+ is more acidic than acetic acid, thus, the equilibrium is shift to left.

2.
By comparing the stability of acetic acid and acetate, because there is delocalization of electrons presented in acetate between O-C-O atoms, acetate gains extra stability, so, the equilibrium shifts to the side (right) with more stable product.

Are there any problems in these two explanations?

Thanks!

By the way, I have a question about comparing the stability of acetic acid and acetate. In acetate, because of delocalization of electrons, the -ve charge is being diminished by resonance effect. However, acetate is still got a -ve charge although it is smaller than 1.

On the other hand, acetic acid is neutral (no charge), so, is acetic acid more stable than acetate?

But, if I compare the stability of phenol and phenoxide, both have resonance effect, and phenoxide is more stable than phenol, because in phenol, energy is needed to separate unlike charges.

This time, which one is more stable, phenol and phenoxide?


By the way, why there is charges separation in phenol (I know the mechanism)? Unlike charges should be attracted together naturally, so, is resonance effect really existed in phenol?

From this reaction:
CH3COOH  +  H2O  <=>  CH3COO-  +  H3O+

In this case, if I add much water into the system, will the equilibrium shifts to right hand side?

I would like to know that water does not involve in the acid dissociation constant, Ka, is it because water is excess?

And why someone said the concentration / density of water does not change? (but it is true that water has changed its concentration in the reaction)

Density of water is depended on temperature because of changes in packing pattern / efficiency with temperature (e.g. ice has a lower density than water, 4 Degree Celsius has the highest density).

In a mixture, water mixed with its immiscible liquid, that both have same amount, let's say 200 mL each. Because they are not miscible, two layers of liquids are formed and now, water molecules only have interaction between themselves, so the packing of water molecules is still the same as pure water.

But when water mixed with its miscible liquid and each of them has the same volume, 200mL. There is interaction between water molecules and the molecules of that liquid, let's say "liquild A". The packing of water molecules is not as same as the pure water anymore, because there are liquild A molecules existed between water molecules. Now, the density of water is equal to its mass (200g) over total volume (400mL). Therefore, the density of water becomes half of its original density. Am I correct?

(2 cases are undergone in constant temperature)  

I used density because someone said that the concentration and the density are related to each other by doing some calculations. (e.g. density = mass / volume)

Is this method not quite suitable to explain the (nearly) unchanged concentration of water?

Thanks a lot!

You said acetic acid is more stable because it has more bonds, you meant the sigma bond, right?

I found that benzene is more stable than cyclohexadiene, but cyclohexaidene has more bonds.

Benzene gains extra stability because there are delocalization of electrons in the ring (resonance effect). Acetate also has resoanace effect. So, can I determine the stability of acetic acid and acetate (phenol and phenoxide ion) just by the number bonds?

Is there any alternative method?

Acid-base reaction:

CH3COOH  +  H2O  <===>  CH3COO-  +  H3O+
___acid__________________conjugate base_______

I found 2 explanations about the shift of equilibrium.

1.
The pKa value of hydronium ion (H3O+) is -1.7, while acetic acid is 4.7.
H3O+ is more acidic than acetic acid, thus, the equilibrium is shift to left.

2.
By comparing the stability of acetic acid and acetate, because there is delocalization of electrons presented in acetate between O-C-O atoms, acetate gains extra stability, so, the equilibrium shifts to the side (right) with more stable product.

Are there any problems in these two explanations?

Thanks!

By the way, I have a question about comparing the stability of acetic acid and acetate. In acetate, because of delocalization of electrons, the -ve charge is being diminished by resonance effect. However, acetate is still got a -ve charge although it is smaller than 1.

On the other hand, acetic acid is neutral (no charge), so, is acetic acid more stable than acetate?

First of all, we are refering to acetic acid in aqueous solutions...acetic acid is considered a moderately strong acid (weak relative to some other acids) and one can see this from different perspectives.  

The conjugate base is stabilized by resonance, the negative charge is somewhat delocalized and thus it has decreased reactivity as a base, to react in the reverse direction.  

Also the acidic hydrogen is bonded to an oxygen group, increasing the charge separation and thus facilitating the reaction; free energy of activation.