Energy Diagrams

[member232]

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Quick question:

When you have an energy diagram for a reaction, and x vs y is labeled "Time vs Energy Level" how do you know the graph is representing enthalpy (H) and not Gibbs free energy (G)?

an example of an energy diagram is http://www.simsoup.info/SimSoup/Potential_Energy_Profile.png (except in my example the axis is labeled "energy level" not potential energy)

I know the distinction between exergonic processes and exothermic processes, but I'm just wondering how you're supposed to interpret "Energy Level" to mean Enthalpy and not Gibbs Free Energy....

Thanks!

 

[stevenz]

Unless otherwise stated, you are safe to assume that it means Gibbs free energy. In reality though, they will probably ask you questions about whether or not something is exothermic/endothermic. In this case, you can more or less assume that contribution from the TdS term (dG = dH - TdS) is negligible and your Gibbs free energy is interchangeable with enthalpy.

 

[member232]

That's what I thought, TBR CBT 5 said it meant change in enthalpy :/

 

[Donald Kimball]

So, given an energy diagram could you simultaneously say that the reaction is spontaneous and exothermic (or non-spontaneous and endothermic)?