Strong Acid Reactions: Explaining HCl + H2O → Cl- + H3O+

[MathewsMD]

For a reaction like HCl + H₂O → Cl^- + H₃O⁺, why is this reaction heavily favoured to the right in water?

I've heard explanations that the products on the right are stabilized by the polar water molecules (considering aqueous solution). I'm just struggling to fully understand this because the reactants on the left seem much more stable since they are all neutral and have stable octets (or 1s orbitals full for the hydrogens). I just don't quite see why the products that are charged would be favoured since charge leads to a molecule in a more reactive and higher energy form...

Any explanations to help better understand this concept would be greatly appreciated!

Also, just to confirm, would this reaction be more favoured to the left given a nonpolar solvent?

I've heard relative acidities always stay the same (i.e. HCl will always be more acidic than CF₃H). Is this statement true and absolute for all compounds and mediums? I can't help but think that there are exceptions where the solvent could possibly react with various compounds differently, giving different acidic properties.

 

[happysmiles36]

For a reaction like HCl + H2O → Cl- + H3O+, why is this reaction heavily favoured to the right in water?

I've heard explanations that the products on the right are stabilized by the polar water molecules (considering aqueous solution). I'm just struggling to fully understand this because the reactants on the left seem much more stable since they are all neutral and have stable octets (or 1s orbitals full for the hydrogens). I just don't quite see why the products that are charged would be favoured since charge leads to a molecule in a more reactive and higher energy form...

I like to think of it more as in that the H2O is polar (has dipole) so the O has a partial negative charge and the H has a partial positive charge. These dipoles make water strong at taking apart compounds with charge.

In HCl, the H holds a partial positive charge and the Cl holds a partial negative charge.

As a result of these two cases, the O in H2O pulls the H from Cl and the H in H2O pulls the Cl from the H. H+ combines with H2O and forms H3O because the H+ ion is highly reactive. Since the pull of all the water molecules surrounds the Cl- ions, equilibrium tends to the right. The HCl covalent bond is also quite weak so it is much easier to pull the HCl apart than it is to reform it. This is why almost 100% of HCl is ionized.

Note that all the compounds in your equation have octets.Any explanations to help better understand this concept would be greatly appreciated!
You should read on Bronsted Acid and Bases, Lewis acid and Arrhenius Theory. You may also want to look at equilibrium constants.Also, just to confirm, would this reaction be more favoured to the left given a nonpolar solvent?
No, if the solvent is non polar then there is nothing causing the covalent bond between H and Cl to break.

I've heard relative acidities always stay the same (i.e. HCl will always be more acidic than CF3H). Is this statement true and absolute for all compounds and mediums? I can't help but think that there are exceptions where the solvent could possibly react with various compounds differently, giving different acidic properties.

*I am not too sure on this one, but here is my take!*

Yes this is always the case because acids are organized by how readily it "donates" a proton and HCl will always be better at it than CF3H. It doesn't matter what compound it is in because you are comparing the acidity relative to each other unless you are talking about a entirely different kind of reaction which would make the acidity part pretty much irrelevant. The more acidic a acid is, the more hydronium ions there will be and this is dependent on the ability for the acid to give up protons. Hopefully I answered this well enough, haven't done chemistry in a while

 

[MathewsMD]

Also, just to confirm, would this reaction be more favoured to the left given a nonpolar solvent?
No, if the solvent is non polar then there is nothing causing the covalent bond between H and Cl to break.

I've heard relative acidities always stay the same (i.e. HCl will always be more acidic than CF3H). Is this statement true and absolute for all compounds and mediums? I can't help but think that there are exceptions where the solvent could possibly react with various compounds differently, giving different acidic properties.

*I am not too sure on this one, but here is my take!*

Yes this is always the case because acids are organized by how readily it "donates" a proton and HCl will always be better at it than CF3H. It doesn't matter what compound it is in because you are comparing the acidity relative to each other unless you are talking about a entirely different kind of reaction which would make the acidity part pretty much irrelevant. The more acidic a acid is, the more hydronium ions there will be and this is dependent on the ability for the acid to give up protons.


Hopefully I answered this well enough, haven't done chemistry in a while

Just to confirm, don't you mean yes? To clarify, the HCl and water will remain in their current, uncharged forms.

Yep, that's more or less what I've heard. I just can't help but think there are special solvents and compounds where the molecular size and structure make the acid more permeable to the solvent to make dissociation easier compared to another one which has a more closed structure in the specific medium. I am still learning about molecular structures, but maybe something to the effect of the actual conformation also changing at different temperatures or pH, as to allow ionization to occur more readily in that environment.

Your insight is appreciated!

 

[happysmiles36]

Just to confirm, don't you mean yes? To clarify, the HCl and water will remain in their current, uncharged forms.

For the non polar solvent, if it is non polar, it doesn't pull on the HCl and won't do anything to separate them into ions, so I mean no. Non polar -> no partial charges. Water is not a non polar solvent, HCl and water (the original equation) will move towards the right side because of water being polar and what I said earlier. In context of a acid reaction, there would be none, no favoring, nothing changes.
ex. (just an example in terms of acid reaction, not sure if this is what happens but you get the gist of it)

HCl + C8H18 -> No reaction

This is mainly because when you talk about HCl and water, the water is a base in this case and can accept H+ and is polar because of the O-H bonds.

Yep, that's more or less what I've heard. I just can't help but think there are special solvents and compounds where the molecular size and structure make the acid more permeable to the solvent to make dissociation easier compared to another one which has a more closed structure in the specific medium. I am still learning about molecular structures, but maybe something to the effect of the actual conformation also changing at different temperatures or pH, as to allow ionization to occur more readily in that environment.

The only thing that would really make acids stronger would be having a more polar solvent than water from what I can think of. The only thing I can think of straight off the top of my head is this (Somewhat of what you are thinking of):
http://en.wikipedia.org/wiki/Piranha_solution#Mechanism_of_action
Changing temperature would really only make the reaction happen faster unless you got to a point where it changed the structure.

Your insight is appreciated!

Thanks

 

[LudusRex]

I can provide some insights into this reaction and why it is heavily favored to the right in water.

First, let's understand the reaction itself. HCl is a strong acid, meaning it dissociates completely in water, releasing H+ ions. This reaction can be represented as HCl + H2O → H+ + Cl-. The H+ ions then combine with water molecules to form hydronium ions (H3O+). Therefore, the overall reaction is HCl + H2O → Cl- + H3O+.

Now, why is this reaction heavily favored to the right in water? This is because of the stabilization of the products by the polar water molecules. Water is a highly polar molecule, with a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. The Cl- ion, being negatively charged, is attracted to the partially positive hydrogen atoms of water, while the H3O+ ion, being positively charged, is attracted to the partially negative oxygen atom of water. This attraction between the ions and water molecules helps to stabilize the products and drives the reaction to the right.

You are right in saying that the reactants on the left seem more stable since they are neutral and have stable octets. However, in this case, the stability of the products is not due to the octet rule, but rather the electrostatic interactions between the ions and water molecules. The charged products may seem to be in a higher energy state, but the overall energy of the system is reduced due to the stabilization by water molecules.

Now, if a nonpolar solvent is used, the reaction may not be as heavily favored to the right. This is because nonpolar solvents do not have the same polar interactions with the ions, and therefore the products may not be as stabilized. This can lead to a lower yield of products and a more balanced reaction.

Regarding the statement about relative acidities always staying the same, it is generally true for most compounds and mediums. This is because the relative acidities are determined by the strength of the acid itself, and not the solvent. However, there may be some exceptions where the solvent can affect the acid strength, such as in the case of superacids. But for most compounds and mediums, the relative acidities remain the same.

I hope this helps to clarify the concept. Chemistry can be complex and there may be exceptions to certain rules, but understanding the basic