The enthalpy of neutralization of HCl with NaOH is -55.8 kJ/mol when very dilute solutions are mixed, but is -58.2 kJ/mol when 2M solutions are mixed, as in this experiment. The reaction is
H+(aq) + OH-(aq) --> H2O(l)
in both cases. Assuming that the enthalpy of water is nearly independent of electrolyte concentration, is the enthalpy per mole of the ions higher or lower in concentrated solutions?