Why does the neutralisation of any strong acid in an aqueous solution by any strong base always result in a heat of reaction of approximately –57 kJ mol−1?
Definition of enthalpy of neutralization: CHANGE IN ENTHALPY WHEN ACIDS AND BASES REACT TOGETHER AND FORM 1 MOLE OF H2O
Strong acids and bases have 100% dissociation in water, meaning that 1mol of water is formed from the reaction of any two (1mol quantities of) strong acids and bases
Notice that the definition of the neutralization of enthalpy is based on moles of water formed; we don't care about the salts
Thus, enthalpy of neutralization is constant regardless of the strong acids or based used