Explaining why some reactions are spontaneous at certain temperatures

[ampakine]

On an exam I got this question:
[PLAIN]http://img849.imageshack.us/img849/5732/spontaneity.png
but at the time I had no idea how to answer it. I still don't really know if I can answer it. I can explain it mathematically with the equation: ΔG = ΔH - TΔS seeing as a spontaneous reaction requires a negative change in G and therefore if the sign of ΔH and ΔS are different then temperature will be a determining factor as to whether or not ΔG will be negative. I have no idea what I would need to plot on a graph though. As for examples of reactions of each type I suppose I needed to have a few example reactions memorised.

 

[Mapes]

I have no idea what I would need to plot on a graph though.

How about plotting ΔH, -TΔS, and their sum?

 

[ampakine]

Oh yeah didn't think of that. I could also plot T vs. their sum.