Question

The molar enthalpy of neutralization of hydrochloric acid, sulfuric acid, and phosphoric acid reacting with sodium hydroxide is −55.8 kJ/mol, −111.7 kJ/mol, and −167.5 kJ/mol, respectively.

(a) Write a chemical equation for each of those neutralization reactions.

(b) Compare the molar enthalpies of neutralization of hydrochloric acid, sulfuric acid, and phosphoric acid. Discuss the similarities and differences among these values.

Answer 1

Chemical reaction

Actually the molar enthalpies of neutralisation of all strong acid with strong base is same i.e - 55.7 kJ/mol, Neutralisation is simply a reaction between H + ion given by acids and OH- ions given by base to form one mole of H2O, since strong acid and strong base completley ionize in aqueous solution number of H(+) and OH(-) produced by 1 gram equivalent of strong acid and strong base is always the same. Hence enthalpy of neutralizationbetween a strong acid and strong base is always constant.

But if change the concnetration of the acid with respect to the base the molar enthalpies of neutralisation varies as we see in case of sulphuric acid and phosphoric acid