Abstract: The general formulas for the basic thermodynamic parameters are revisited (entropy, free energy and others) form point of view of the speed of a sound determining dependence on pressure and temperatures in nonideal environments. As an example a behaviour of speed of a sound is investigated as functions of temperature and pressure for Van der Waals gas. A comparison of the results of evaluation with the available experimental data is carried out. The analysis has shown, that received formulas describe the velocity of a sound in a wide range of pressures and temperatures.