Energy Diagrams

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