Why does a weak acid have a higher heat of nutralization when reacting with a base, than a strong acid?

Question

Example: NaOH reacting with HCl(strong) has a heat of reaction of -41.8, and NaOH reacting with acetic acid(weak) has a heat of reaction of 41.98.

Answer 1

The heat of reaction for all strong base-strong acid neutralizations are almost identical. The strong bases and acids are ionized almost 100% (they are strong electrolytes). Ignoring spectator ions the reaction is:

H+(aq) + OH- (aq) = H2O (l) or something similar.

For weak acids, the heat of ionization for the weak acid must be considered. This is Hess's Law. The heat of reaction is the heat of ionization of the acid plus the heat of neutralization.

Answer 2

The heat of neutralisation of a strong base with a strong acid is actually the heat of formation of water. All the neutralisation reactions involving the reaction of a strong base with a strong acid have near about the same enthalpy of neutralisation(-57kJ/mol)
now let us apply Hess's law of constant heat summation,
let BOH be the base & HA be the acid,
ignoring the common heats that are same is case of both weak acid;strong base &strong acid;strong base .

BOH(aq)=B+(aq)+OH-(aq) ;ΔH1
HA(aq)=H+(aq)+A-(aq);ΔH2
H+(aq)+OH-(aq)=H20(l); ΔH3

in case of strong electrolytes ΔH1&ΔH2 vanish(they r present in the solution as ions), but in case of weak electrolytes ΔH1 or ΔH2 or both has significant values, they sum up with ΔH3(it is common for both the cases), to make the enthalpy in case of weak electrolytes higher.

In weak electrolytes the H+ or OH- ion is bound strongly to the rest of the molecule to make the dissociation energy high.

Answer 3

Acids and bases react so straight away that the two will react by way of fact the backside is extra to the mixture. between drops of base the two acids will combat it out to realize their equilibrium concentrations; the good acid will win. in spite of everything the good acid is fed on, the susceptible acid will then be neutralized. interior the state of affairs you provide - organic and organic separation schemes, you %. a susceptible base which will merely react with the greater suitable acid. ie NaHCO3 will react with carboxylic acids (susceptible acids) yet no longer with the even weaker phenols. subsequently NaHCO3 will do away with a carboxylic acid selectively; NaOH can then ionize and do away with a phenol. Addition of an acid will, in turn, ionize the backside making it water soluble. This leaves merely the impartial compound on your organic and organic layer.

Answer 4

The bond to the H atom which ionises off as H+ must be broken. The weaker the acid, the stronger that bond, and the less the enthalpy of neutralisation.

NaOH and HCl, by the way, is about -57kJ/mol.