The molar solution enthalpies of ionic liquids (IL) EMIBF4 (1-methyl-3-ethylimidazolium tetrafluoroborate), EMIC (1-methyl-3-ethylimidazolium chloride) and ionic solid NaBF4 at various molalities were determined by the solution-reaction isoperibol calorimeter in water at 298.15 K. In terms of a Debye-Huckel limiting term, the molar solution enthalpies of EMIBF4, EMIC and NaBF4 at infinite dilution, A, H, were obtained. Then the values of apparent relative molar enthalpy were calculated. Hydration heat of both cation EMI+ and anion BF4- was discussed. In terms of values of Delta H-s(m)degrees, the reaction heat of NaBF4 + EMIC ->. EMIBF4 + NaCl was estimated. (c) 2006 Elsevier B.V. All rights reserved.