thermodynamic tables and charts may be used when both H and S are tabulated. since G=H-TS , at constant temperature , deltaG=RT LOG(f2/f1)= delta H- t*deltaS. if state 1 is at loe pressure where the gas is ideal , then f1=P1 , RTlog(f2/P1)= deltaH -T*deltaS, where the subscript indicates states. use this method to determine the fugacity of steam at 400 C AND 15 MPa. what value does the fugacity coefficient have at this pressure