A good source for formation data for compounds is the NIST Chemistry Web Book site. Values of ΔH°f, but not of ΔG°f are reported. Instead, values of absolute standard entropies S° are listed for compounds and elements. To illustrate the use of NIST data, let H2O2 be the compound of interest. Values provided by the Chemistry Web Book:
• ΔHofH2O2(g)] = -136.1064 kJ mol-1
• S°[H2O2(g)] = 232.95 J mol-1 K-1
• S°[H2(g)] = 130.680 J mor-1 K-1
• S° [O2(g)] = 205.152 J mol-1 K-1
All data are for the ideal-gas state at 298.15 K and 1 bar. Determine a value for ΔGof298 for H2O2 (g).