A thermodynamic relation, defined to improve methodologies in the Second Law Analysis of thermal systems, is studied. This relation is defined by dividing the specific thermomechanical exergy by the specific enthalpy of a substance, adopting as reference a selected thermodynamic state. This relation is determined and analyzed for liquid water and steam in a range of temperatures (30°C - 700°C) and pressures (0.101325 MPa - 18.1 MPa). The behavior of the proposed relation is compared against the exergy behavior as a function of temperature and pressure. The proposed relation can be used to compare and evaluate thermodynamic states that have similar exergy content. It makes possible the identification of states presenting higher exergetic level per enthalpy unit. The variation of partial derivatives (temperature and pressure) of the specific thermomechanical exergy for superheated steam is analyzed. The variation of partial derivatives of the thermodynamic relation between the exergy and enthalpy (adopting as reference a selected thermodynamic state) is also studied. These derivatives are determined for sub-cooled liquid water and superheated steam in a range of temperatures (200°C - 700°C) and pressures (2 MPa - 18 MPa). The behavior of the partial derivatives is compared and discussed against the variation of enthalpy and entropy, considering the effects of temperature and pressure variations. The analysis performed in this work can help to improve methodologies in the Second Law Analysis of thermal systems. The aspects focused upon can be useful in thermodynamic analysis and optimization of steam cycles and thermal processes.38 97104Bejan, A., Advanced Engineering Thermodynamics, 1988. , John Wiley, New YorkBejan, A., Tsatsaronis, G., Moran, M.J., (1996) Thermal Design and Optimization, , John Wiley, New YorkFrangopoulos, C.A., Optimal Design of a Gas Turbine Plant by a Thermoeconomic Approach (1988) Proceedings, ASME COGEN TURBO POWER' 88, 3 IGTI, pp. 369-375. , G.K. Sevory and T.H. Franson, eds., ASMEKeenan, J.H., Keyes, F.G., Hill, P.G., Moore, J.G., (1978) Steam Tables: Thermodynamic Properties of Water, Including Vapor, Liquid, and Solid Phases (SI Units), , John Wiley, New YorkLlagostera, J., Subrotinas computacionais de elevada exatidão para determinação de propriedades termodinâmicas da água (1994) Anais do V Encontro Nacional de Ciências Térmicas, pp. 395-398. , ABCM, EPUSP, São PauloLlagostera, J., Estudo da relação entre entalpia e exergia da água, aplicável à análise energética e exergética de ciclos termodinâmicos a vapor (1995) Anais do XIII Congresso Brasileiro e II Congresso Ibero Americana de Engenharia Mecânica, pp. 1-4. , (CD-ROM, Área: Termociências, Tema: Termodinâmica), ABCM, UFMG, Belo HorizonteMoran, M.J., Sciubba, E., Exergy Analysis: Principles and Practice (1994) ASME Journal of Engineering for Gas Turbines and Power, 116, pp. 285-290Szargut, J., Morris, D.R., Steward, F.R., (1988) Exergy Analysis of Thermal, Chemical and Metallurgical Processes, , Hemisphere, New YorkTsatsaronis, G., Lin, L., Tawfic, T., Gallaspy, D.T., Exergoeconomic Evaluation of a KRW-Based IGCC Power Plant (1994) ASME Journal of Engineering for Gas Turbines and Power, 116, pp. 300-306Valero, A., Lozano, M.A., Serra, L., Torres, C., Application of the exergetic cost theory to the CGAM problem (1994) Energy (Oxford), 19 (3), pp. 365-381