Now we come to the reconsideration of the standard state. The second term of the right-hand side of Equation (16) is the term which includes the fugacity coefficient of the fluid at T and reference pressure Pr. At a pressure of 0, it is possible to treat any fluid like an ideal gas, because neither the particle volume nor intermolecular forces play a role as the particle distances are infinite. If we recapitulate that this term represents the sum (integral) of deviations from a pure real fluid and a pure ideal gas, then the difference of the first two terms in Equation (16) are the thermodynamic properties of an ideal gas 
. Ideal gas properties a designated by an asterisk *
(17)
In other words, if we know the thermodynamic ideal gas properties of a pure phase component and are able to calculate the fugacity coefficient at Pr (having an EOS) we know the properties of the real fluid at Pr or any other P. Most thermodynamic ideal gas properties can be obtained using, for example, ab initio calculations and molecular simulations. Because of the lack of intermolecular forces only single-particle properties and velocity distributions have to be considered to evaluate the inner energy 
and the heat capacity 
. The partitioning function or has to be calculated to obtain the entropy 
. For any fluid phase component, it is convenient to choose the ideal gas as its standard state. In addition, because 
in Equation (17) is a corrected term and not a real quantity, this special choice is also called the standard state of an hypothetical ideal gas. As for solids the reference conditions are usually 0.1 MPa and 298.15 K.
