Question 8.51: positive vs. negative enthalpy

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Heerali Patel 3A
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Question 8.51: positive vs. negative enthalpy

Postby Heerali Patel 3A » Mon Feb 08, 2016 5:43 pm

Question 8.51:
The enthalpy of formation of trinitrotoluene (TNT) is -67KJ/mol, and the density of TNT is 1.65 g/cm^3. In principle, it could be used as a rocket fuel, with the gases resulting from its decomposition streaming out of the rocket to give the required thrust. In practice, of course, it would be extremely dangerous as a fuel because it is sensitive to shock. Explore its potential as a rocket fuel by calculating its enthalpy density (enthalpy released per liter) for the reaction 4C7H5N3O6(s) + 21O3(g) -> 28CO2(g) + 10H2O(g) + 6N2(g).

The answer from the solutions manual is +23.9x10^3 KJ/L. My question is why the sign is positive because the enthalpy of reaction that I get is -13168.48KJ?

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Re: Question 8.51: positive vs. negative enthalpy

Postby Chem_Mod » Tue Feb 09, 2016 12:12 am

Because it asked for the enthalpy released which literally means heat released (exothermic). So the negative sign is not necessary.

Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

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