In enthalpy of neutralisation,we used 1 gram equivalent of an acid and a base. Why not gram moles have been employed?

Dear Student

It is important to note that gram equivalent is used in the heat or enthalpy of neutralisation. This is because neutralisation involves 1 mole of H+ ions and 1 mole of OH- ions in order to produce 1 mole of water and in this process 57.1 kJ of heat gets liberated.
Also,  on complete dissociation of one gram equivalent of various acids, 1 mole of H+ ions are liberated, however, 1 mole of the acid may give rise to one mole of H+ ions in the solution depending upon its basicity.
Therefore, 1 mole of H2SO4 produces 2 moles of H+ ions on complete dissociation, and in case of 3 moles of H+ ions are produced in case of 1 mole of H3PO4 . But when 1 gram equivalent of both ​H2SO4 and ​H3PO4 are taken, then 1 mole of H+ ions are produced.
This is the reason why gram equivalent weight is more appropriate to use in the calculation of enthalpy of neutralisation.


Regards

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