You have a calorimeter with a heat capacity of 0.216 kJ/ºC.  You combine 25.0 mL 2.50 M NaA (A- = conjugate base of weak acid HA) with an equal volume of HCl of higher molarilty.  The temperature changes from 20.4 ºC to 21.9 ºC.  What is ΔHºassoc for the reaction of A- with H+, in kJ?