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 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.