The substance X is an element which has the elemental form of X(s) at 25oC. The standard enthalpy of formation of HXO4(g) is -818.0 kJ/mol at 25oC. The standard entropy of HXO4 (g) and X(s) are, respectively 175.8 J/mol•K and 30.70 J/(mol•K) at 25oC. What is the standard free energy change (kJ) for the following reaction at 504.6 K ? [Note: Answer should be expressed as "xxx.x", or with one sig fig after the decimal point.] 2 HXO4(g) + 7 H2(g) ? 2 X(s) + 8 H2O(g) [Note (all at 25oC): (1) Standard enthalpies of formation for H2O(g) and H2(g) are, respectively, -241.8 and 0 kJ/mol. (2) Standard free energies of formation for H2O(g) and H2(g) are, respectively, -228.6 and 0 kJ/mol. (3) Standard entropies for H2O(g) and H2(g) are, respectively, 188.7 and 130.6 J/(mol•K).]