Thermochemical properties of phase transitions are an important parameter of a pure substance. Traditional methods for determination of this parameter are based on the investigation of the process of transition from the condensed phase to gas at 298.15 K. This procedure is not universal and has some well-known problems, which were discussed in [1]. In this work, we propose a solution calorimetry approach to the determination of the enthalpies of phase transitions directly at 298 K. This approach is based on the well-known relationship between the phase transition enthalpy of compound Ai at 298 K and the enthalpy of solution ( Ai /S soln Δ Н ) and solvation ( Ai /S solv Δ Н ) of compound Ai in solvent S at 298 K: g Ai /S cr(l)Δ Н (298 К) = Ai /S soln Δ Н (298 К) - Ai /S solv Δ Н (298 К) (1) Solution enthalpy can be measured experimentally. The solvation enthalpy can be calculated using the additive scheme as well as the vaporization enthalpy. However it was shown that the solvation enthalpies as well as vaporization enthalpies at 298 K of pyrazole and imidazole have different values despite the same molecular formula. This difference was analyzed based on substituted pyrazoles and imidazoles with the same molecular formula. And it turned out that this difference is a constant and can be taken into account for calculation the solvation enthalpies of substituted imidazoles. Also in the present work we have developed an additivity scheme [2] for the calculation of solvation enthalpy of systems with solute-solvent hydrogen bond interactions. A simple additivity scheme [2] was modified taking into account the contribution of hydrogen bonding on the values of solvation enthalpy. This contribution was calculated using Iogansen equation which connected the enthalpy of hydrogen bonds with frequency shifts of N-H stretching vibrations. The efficiency of the scheme for calculating the enthalpies of solvation was tested on the substituted NH containing compounds. We have determined vaporization/sublimation enthalpies of substituted NH containing compounds at 298.15 K using experimentally measured solution enthalpies and estimated values of solvation enthalpies. The values of vaporization/sublimation enthalpies obtained using the solution calorimetry approach are in good agreement with data from transpiration method and data from the literature.