- #1
yucheng
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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?
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?
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