What is the maximum amount of useful work that can be accomplished under standar

Question

What is the maximum amount of useful work that can be accomplished under standard conditions by this system if 5 mol of ethylene (C2H4) is burned?

I previously calculated delta H to be -7055 kJ.

Explanation / Answer

2H2 + 2C(graphite) ===> C2H4(g) 52.30kJ/mol H2 +1/2 O2 ===> H2O -285.83kJ/mol C(graphite) + O2 ===> CO2 -393.5kJ/mol Also, overall: C2H4 + 3O2 ===> 2CO2 + 2H2O Next, arrange the equations so that they add up to the desired reaction, reversing the sign of the enthalpy for the reverse reaction. Add up all the reactions, and cancel on either side of the equation. C2H4(g) ===> 2C(graphite) + 2H2 -52.30kJ 2O2(g) + 2C(graphite) ===> 2CO2(g) 2x(-393.5kJ/mol) = -787kJ O2 + 2H2 ===> 2H2O 2x(-285.3) = -575.6kJ --------------------------------------… Add the equations, cancel on both sides -52.30 kJ -787 kJ -575.6kJ ------------- -1415 kJ

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