A general and simple state equation for all gases is proposed based on the theory that the elastic collision between the boundary and gas molecules contributes the pressure, whilst the completely inelastic collision contributes the exchange of heat between the gas and the surrounding via boundary. In addition, at the high density and temperature, the high frequency of collision abates the distance of molecular motion, thus the effect of molecular mass is significant. Therefore, the gravity is introduced into the state equation. The general state equation covers the whole temperature range below the critical temperature. The full thermodynamic data of liquid-gas equilibrium at saturation of 39 substances including the light and heavy water are used for the fitting of equation. The general state equation fits the reference data well except the temperature near to the critical temperature. Moreover, the theory is applicable for the liquid, and the calculation of thermodynamic parameters such as the specific heat capacity.

A general and simple state equation for all gases is proposed based on the theory that the elastic collision between the boundary and gas molecules contributes the pressure, whilst the completely inelastic collision contributes the exchange of heat between the gas and the surrounding via boundary. In addition, at the high density and temperature, the high frequency of collision abates the distance of molecular motion, thus the effect of molecular mass is significant. Therefore, the gravity is introduced into the state equation. The general state equation covers the whole temperature range from the melt point to the critical temperature, but is invalid solid near to the critical point including the vapor pressure of solid, liquid and the single gas phase of a substance. 39 substances including the light and heavy water are collected with the full thermodynamic data of liquid-gas equilibrium at saturation. The general state equation fits the reference data well with the errors, <5%, for most of the substances.

A general and simple state equation for all gases is proposed based on the theory that the elastic collision between the boundary and gas molecules contributes the pressure, whilst the completely inelastic collision contributes the exchange of heat between the gas and the surrounding via boundary. In addition, at the high density and temperature, the high frequency of collision abates the distance of molecular motion, thus the effect of molecular mass is significant. Therefore, the gravity is introduced into the state equation. The general state equation covers the whole temperature range below the critical temperature. The full thermodynamic data of liquid-gas equilibrium at saturation of 39 substances including the light and heavy water are used for the fitting of equation. The general state equation fits the reference data well except the temperature near to the critical temperature. Moreover, the theory is applicable for the liquid, and the calculation of thermodynamic parameters such as the specific heat capacity.

A new general state equation for all real gases is proposed based on the theory that the inelastic collision leads the gas molecules to liquefy on the walls of container, thereby affords the exchange of heat between the gas and the surrounding via boundary. Therefore, the state equation of gas is equivalent to the equation of gas-liquid phase equilibrium. Based on the Boltzmann distribution of energy, a new general state equation is established. Moreover, in the critical region, the gravimetric potential is introduced to the state equation. P-V-T data at saturation and isobars of 79 substances are applied for fitting the equation. The fitting results are applaudable. Furthermore, the state equation is applicable for the gas-solid phase equilibrium. A calculation result indicates that the critical region starts from ca. 30-40% and ends with ca. 60-70% of the molar fraction of liquefied portion, irrespective of the molecular mass and interactions. Hence, the critical temperature and extraordinarily large specific heat capacity as well are resulted from the interruption of heat exchange circuit between gas and the surroundings. Academically, the new state equation lays a base-stone for the derivative equations of gas specific heat capacity, sound velocity in the gas, etc.