The following sequence of reactions occurs in the commercial production of aqueous nitric acid: 4NH3(g)+5O2(g)⟶4NO(g)+6H2O(l) ΔH=−907kJ
2NO(g)+O2(g)⟶2NO2(g) ΔH=−113kJ
3NO2+H2O(l)⟶2HNO3(aq)+NO(g) ΔH=−139kJ Determine the total energy change for the production of one mole of aqueous nitric acid by this process
I've seen various solutions online where it says to multiply the reactions in their order by 3,6, and 4 respectively then cancel the duplicates and add the changes in energy to get the answer. My question though is how are they figuring out what to multiply each reaction by.