Question

The enthalpy of neutralisation of oxalic acid by a strong base is -25 kcal/mol tge enthalpy of neutralisation of strong acid and strong base is -13.7 kcal/equiv the enthalpy of dissociation of

Answer 1

Answer: The enthaply of dissociation is 1.2 kcal/equiv

Explanation:

Heat of neutralization defined as heat evolved when one gram equivalent of an acid is completely neutralized by a base.

Strong acid and strong base and the salt produced remain completely dissolved in dilute solutions, so the neutralization reaction may be represented as

$H^++A^-+B^++OH^-\rightarrow H_2O+B^++A^-$

Therefore, the neutralization between strong acid and strong base may also be called as formation of one mole of water. So, the heat change accompanying this reaction is constant and the value is -13.7 kcal/equivalent.

But oxalic acid being a weak acid will not dissociate completely in water. Some of it remains as undissociated molecules in water. Some amount of heat of neutralization is used to ionise undissociated molecules. As some amount of energy is consumed, energy released is less.

As enthaply of neutralization for oxalic acid is given for 1 mole= -25kcal

For 1 equivalent it will be = -25/2 kcal = -12.5kcal (as it is a dibasic acid)

Enthalpy of dissociation = enthaply of neutralization of weak acid- enthalpy of neutralization of strong acid

Enthalpy of dissociation = -12.5 -( -13.7) kcal = 1.2kcal