Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: srahimi on May 01, 2008, 07:38:14 PM
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Using the method of examining the Change and Enthalpy and The Change of Entropy Predict if the reactions are Spontaneous or not.
Reaction ΔH ΔS ΔG
Ice Melting at 20C
Sodium Metal in water at 25C
Water Boiling at 100C
Paper Burning
Water freezing at 0C
CaCO3 Precipitating out when heated
Isothermal Expansion of a gas
What is the Standard Heat of Formation for Octane C8H18?
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You solve those by figuring out the ΔH's and ΔS's, using those in the ΔG equation. If ΔG is negative it means it is either spontaneous or non spontaneous, and if it is positive it means it is either spontaneous or non spontaneous (Not both, for - it is one, and + it is the other. Which is it? That is something you should know. ).
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if i remeber correctly to find the standard heat of formation of C8H18 you add up all the bond energies of formation for all the bonds present the C-C or C-H bonds.. the bond energies should be provided with the question or in the back of the book...
of course you could do it the old fashion way and use a calorimeter and fully burn a know molar amount of the substance and use the number you got in calculating how much it would take to burn one molecule but i believe the first way is much easier...although less entertaining