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In my class we have defined Naphtha as a mixture of hydrocarbons with BP ranging from 30-220 deg-C.

Our desired product is ethylene through thermal cracking. I have drawn the mechanism here:



My Questions:

1) How can we determine what temperature to use to effectively crack this? I read in a paper that they apply this formula:
dH_reactor = dH_ethylene - dH_naphtha

So we are just taking the different between our desired product and feedstock's heat of formation. So how does one get the heat of formation for Naphtha when it is a MIXTURE of gasses? I don't need to know exactly how to do it for my purposes, but just a point in the right direction.


2) My second question is about the mechanism I drew. As it is drawn, the reaction should go to 100% completion in theory. However, this does not happen. This is because we see side reactions between olefins and radical species which give us secondary products. We minimize this by adding H2O to dilute the reactants and lower the partial pressure of our hydrocarbons. If I was to say this promotes UNIMOLECULAR kinetics, would I be using that word correctly?

Thank you!