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 -893.6 kJ/mol at 25oC. The standard entropy of HXO4 (g) and X(s) are, respectively 152.7 J/mol•K and 22.10 J/(mol•K) at 25oC. What is the standard free energy change (kJ) for the following reaction at 499.0 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)