Why are more polarized bonds weaker (Acid dissociation)?

Thread starter yucheng
Start date Aug 7, 2023
Tags

Polarity

Click For Summary

The discussion centers on the acidity of hydrofluoric acid (HF) and the comparison of bond strengths between H-F and H-I. It highlights that the weak acidity of HF in dilute solutions is attributed to the strong H-F bond and the high dissolution enthalpy of HF, which offsets the negative enthalpy of hydration of the fluoride ion. The argument that the H-F bond is stronger than the H-I bond is based on bond enthalpies, but for acid dissociation, one must consider the formation of ions and their hydration, suggesting that the initial argument may be oversimplified. Additionally, the discussion touches on the influence of electron-donating groups on the O-H bond strength in carboxylic acids, noting that these groups can reduce bond polarity and thus increase bond strength. The relationship between bond polarity and strength is questioned, with a focus on why polar bonds tend to be weaker than non-polar bonds.

Aug 7, 2023

yucheng

Wikipedia says that:
The weak acidity in dilute solution is sometimes attributed to the high H—F bond strength, which combines with the high dissolution enthalpy of HF to outweigh the more negative enthalpy of hydration of the fluoride ion.
(https://en.wikipedia.org/wiki/Hydrofluoric_acid)
(the H-F bond is highly polar compared to the H-I bond)
(H-F bond is stronger than H-I bond)

It is a common argument to say that H-F bond is stronger than H-I bond on the basis of bond enthalpies:

$$\text{HX} -> \text{H(g)} + \text{X(g)}$$.

However, for dissociation of acids, we must actually consider (hence the electron affinity comes in)

$$\text{HX} -> \text{H}^+(g) + \text{X}^-(g)$$,

and then the hydration of the ions, no? Does this mean the argument given above is... inaccurate, though it works?
____________
For O-H bonds in carboxylic acids, electron donating group causes the O-H bond to be less polar hence stronger.
Carboxylic acids, https://en.wikipedia.org/wiki/Inductive_effect

Why Is polarity related to bond strength? Why are polar bonds weaker than non-polar bonds?

Last edited: Aug 7, 2023

Thread 'Molecular-level explanation of macroscopic phenomena: dissolving'

What I know and please correct me: a macroscopic probe of raw sugar you can buy from the store can be modeled to be an almost perfect cube of a size of 0.7 up to 1 mm. Let's assume it was really pure, nothing else but a conglomerate of H12C22O11 molecules stacked one over another in layers with van de Waals (?) "forces" keeping them together in a macroscopic state at a temperature of let's say 20 degrees Celsius. Then I use 100 such tiny pieces to throw them in 20 deg water. I stir the...

View full post »