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8.57

Posted: Sun Jan 14, 2018 6:42 pm
by PranithaPrasad
the question wants us to find the reaction enthalpy for the hydrogenation of ethyne to ethane which is
C2H2 + 2H2 --> C2H6. Then it gives us the enthalpies of each element. What I did was use the sum of the products - the sum of the reactants, but the answer book did something else and the answer was different. Can someone explain what we would have to do and why we can't use the products - the reactants in this situation?

Re: 8.57

Posted: Sun Jan 14, 2018 7:24 pm
by Emily Oren 3C
You can only use the products-reactants method if you are given the heats of formation and this problem gives heats of combustion instead. The answer book manipulates (adds, reverses, multiplies by a constant) the given combustion equations until getting the equation: C2H2 + 2H2 --> C2H6. The same operations are done to the heats of combustion in order to get the answer in the book.