H2 + co2 → ch2o2 reactant bond energies: h–h is 432 kj/mol, c=o is 799 kj/mol product bond energies: c–h is 413 kj/mol, c=o is 745 kj/mol, c–o is 358 kj/mol, o–h is 467 kj/mol how much energy must this system absorb before the reaction can begin?.