Explaining why some reactions are spontaneous at certain temperatures

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SUMMARY

The discussion centers on the spontaneity of reactions at varying temperatures, specifically using the Gibbs free energy equation: ΔG = ΔH - TΔS. A spontaneous reaction is characterized by a negative ΔG, which occurs when the signs of ΔH and ΔS differ. The temperature (T) plays a crucial role in determining the sign of ΔG, making it essential to understand how to graphically represent ΔH, -TΔS, and their sum to visualize this relationship effectively.

PREREQUISITES
  • Understanding of Gibbs free energy and its significance in thermodynamics
  • Familiarity with the concepts of enthalpy (ΔH) and entropy (ΔS)
  • Basic graphing skills to plot thermodynamic functions
  • Knowledge of spontaneous reactions and their criteria
NEXT STEPS
  • Learn how to graphically represent thermodynamic equations, specifically ΔH and -TΔS
  • Study the implications of temperature on reaction spontaneity
  • Explore examples of spontaneous and non-spontaneous reactions
  • Investigate the role of entropy in chemical reactions
USEFUL FOR

Chemistry students, educators, and anyone interested in understanding thermodynamics and reaction spontaneity in chemical processes.

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

How about plotting ΔH, -TΔS, and their sum?
 
Oh yeah didn't think of that. I could also plot T vs. their sum.
 

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