[srahimi]

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 20C
Sodium Metal in water at 25C
Water Boiling at 100C
Paper Burning
Water freezing at 0C
CaCO3  Precipitating out when heated
Isothermal Expansion of a gas



What is the Standard Heat of Formation   for Octane C8H18?

[enahs]

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. ).

[mnakhla]

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