A general and simple state equation for all gases

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.