A New Thermodynamics

By Kent W. Mayhew

Enthalpy: What is It   By Kent W. Mayhew        


You should read my internal energy block before this one


Consider the enthalpy (H) relation:


       H=E+PV       1)


where E is the internal energy of the system, while P and V are wrongly thought to be the system's mechanical parameters pressure and volume respectively 


As was previously discussed in the blog on entropy and internal energy we could rewrite eqn 1) in terms of entropy and temperature as: 


       TS=H=E+PV     2)


Enthalpy Issues

Reconsider physical chemistry where enthalpy (H=E+PV) helps with our understanding of reactions. Again enthalpy change should be limited to isothermal chemical reactions that involve isobaric volume change i.e. Lost Work. And it is because of the energy associated with lost work in reactions that experience volume increases that this version of enthalpy change remains necessary:

   dHsys = dEsys+ (PdV)atm   =  dEsys+ PatmdVsys       3)

 Again one might ask; should enthalpy change is be written because when considering the energy changes within a system because PdV is external (surroundings) while dE is internal to the system.

Now the above is going to scare those indoctrinated with traditional ways of dealing with chemical reactions.  All I can say is do not blame the messenger! And yes I am sorry but your mature science is in dire need of an overhaul if you ever want to simplify it i.e. end its existence as a complication of our reality.

Again in terms of energy in 3) should be rewritten as:

dQin = dHsys = dEsys + (PdV)atm   =  dEsys + PatmdVsys       4)

 Obviously there are issues with enthalpy. This does not mean that enthalpy does not belong in physical chemistry rather it means our understanding must change i.e. see Physical Chemistry









Enthalpy: What is it
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Sommerfield quote:"Thermodynamics is a funny subject. The first time you go through it, you don't understand it at all. The second time you go through it, you think you understand it, except for one or two small points. The third time you go through it, you know you don't understand it, but by that time you are so used to it, so it doesn't bother you any more."
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