Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: escapeartistq on May 24, 2005, 06:21:48 PM
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Prove that 2C8H18(l) + 25O2(g) -> 16CO2(g) + 18H2O(g)
is exothermic, admiting that all gases behave like ideal gases.
I tried this:
?U = ?H + W
W = -RT?n
?n = (16+18) - 25 = 9
so W < 0
How do you prove that AH < 0 as asked?
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Use Hess's law to determine the heat of reaction.
http://energy.sdsu.edu/testcenter/testhome/Test/solve/basics/tables/tablesComb/formation.html
this site has some heats of formations that you can use to determine the heat of reaction.
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Thanks, for your suggestion. Now I see it was a stupid question because I thought there was a way to show that AH < 0 without recurring to Hess's law.