Abstarct: In the present study, the thermodynamic properties of the formation reaction of hydrogen chloride from chlorine gas were calculated and hydrogen gas using the modified Manning-Rosen potential energy model and by using the specific thermodynamic relationships that exist between the components of a gas compound. In a temperature range of 200 to 1000 K. The thermodynamic properties calculated from the modified Manning-Rosen potential model were compared with the available experimental results, the coordinate oscillator model calculations, and the Tietz and Rosen-Morse potential energy models in the studied temperature range. The obtained results enthalpy, entropy, internal energy, Gibbs and Helmholtz free energy of gases of hydrogen, chlorine and hydrogen chloride showed that the used potential model is able to predict the thermodynamic properties of diatomic gases faveroitly. Also, the results obtained for the formation reaction of hydrogen chloride in comparison with the available experimental values showed that the proposed model is in a good agreement with the experimental values. The importance of this model for predicting thermodynamic properties is that it requires only three molecular spectroscopy parameters including dissouation energy, equilibrium bond length, and equilibrium vibrational frequency. The results of the proposed model can also be used to improve the thermochemical data of the quantum computations baxsed on the harmonic oscillator model.