How can I use standard entropies and heats of formation to calculate ΔGƒ° at a certain temperature (°C)?

Question

Use standard entropies and heats of formation to calculate ΔGƒ° at 25°C for the following compounds:

a) ammonium nitrate (s)

b) chloroform, CHCl3(l)



c) potassium chloride (s)

Answer 1

∆Gº = ∆Hº = T∆Sº

Look up the values for ∆Hº and ∆Sº for each of the compounds and plug them into the equation above. The T (temperature) is 298K and don't forget to change ∆Sº values to kJ/Kmol instead of the usually given J/kmol. Or, of course, you could change the ∆Hº values from kJ/mol to J/mol. Either way, just make sure the units are the same.