Why is the Enthalpy of Neutralisation for HF Greater than 68KJ?

[theincrediblea]

why enthalpy of neutralisation of HF is greater than 68KJ.

MY attempt

Enthalpy of neutralisation= Enthalpy of Ionisation + Δ(H+ + OH-)

Now,For very strong acid, enthalpy of Ionisation = 0,

Hence enthalpy of neutralisation= (H+ + OH-)= -13.7KCal

for weak acid, enthalpy of ionisation is always > 0

∴, enthalpy of neutralisation should always be less than 13.7 (57 KJ).

Please explain

 

[Adithyan]

HF + OH- = F- + H2O

Enthalpy of this reaction = Enthalpy of neutralization of HF = Enthalpy of products - Enthalpy of reactants
which comes out to be greater than 68kJ. So, here evidently the enthalpy of of ionization of HF is EXOTHERMIC.

Hope this helps! :)
-Adithyan

 

[Borek]

Now,For very strong acid, enthalpy of Ionisation = 0

That's not true.

Just because the acid dissociated long ago and the solution temperature got in equilibrium with the surroundings, doesn't mean enthalpy of ionization was zero.

 

[theincrediblea]

thanks adithyan for ur help

 

[LudusRex]

further

The enthalpy of neutralisation is a measure of the energy released or absorbed when an acid and a base react to form a salt and water. It is a thermodynamic property that depends on the strength of the acid and base involved in the reaction.

In the case of HF, it is a weak acid, meaning that it does not completely ionize in solution. This means that the enthalpy of ionisation for HF is greater than 0. This leads to a larger contribution to the overall enthalpy of neutralisation, resulting in a higher value than the theoretical value of 13.7 kcal (or 57 kJ).

Furthermore, the strength of an acid is also related to its bond strength. HF has a very strong bond between the hydrogen and fluorine atoms, making it more difficult to break and release the hydrogen ion. This results in a higher enthalpy of ionisation and therefore a greater enthalpy of neutralisation.

In contrast, a strong acid like HCl has a weaker bond between the hydrogen and chlorine atoms, leading to a lower enthalpy of ionisation and a lower enthalpy of neutralisation. This is why the enthalpy of neutralisation for HF is greater than 68 kJ, as it is a weaker acid with a stronger bond.