Given the following at 25C, calculate Hf for HCN(g) (in kJ/mol ) at 25C. 2NH3(g)+3O2(g)+2CH4(g)2HCN(g)+6H2O(g)H=870.8kJ H=80.3kJ/mol for NH3(g),74.6kJ/mol for CH4, and 241.8kJ/mol for H2O(g)