The standard molar enthalpy for the formation of diborane (B2H6) cannot be determined directly because the compound cannot be synthesized from its elements. Calculate Hf for diborane from the following:

3 H2O (g) 3 H2 (g) + 3/ 2 O2 (g) B2O3 (s) 2 B (s) + 3/2 O2 (g) B2O3 (s) + 3 H2O (g) B2H6 (g) + 3 O2 (g)

Hrxn = 725. 4 kJ Hrxn = 1271.9 kJ Hrxn = 2032.9 kJ