Thermodynamics & PV work relationships

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SUMMARY

This discussion focuses on the relationships between enthalpy (ΔH), internal energy (ΔU), heat (q), and work (W) in thermodynamics, particularly under constant pressure (P) and constant temperature (T) conditions. The user seeks clarity on the equations ΔU = W + q and dH = dU + d(PV), emphasizing their importance in determining U and H for specific processes. Additionally, the user expresses confusion regarding the conditions under which Δ values equal zero, indicating a need for a clearer understanding of these thermodynamic principles.

PREREQUISITES
  • Understanding of thermodynamic concepts such as enthalpy and internal energy
  • Familiarity with the first law of thermodynamics
  • Knowledge of heat transfer mechanisms at constant pressure and volume
  • Basic grasp of reversible and irreversible work (Wrev and Wirr)
NEXT STEPS
  • Study the derivation and applications of the first law of thermodynamics
  • Learn about the conditions under which ΔH and ΔU are equal or zero
  • Explore the implications of constant pressure and constant volume processes in thermodynamics
  • Investigate the significance of the dH = dU + d(PV) equation in various thermodynamic cycles
USEFUL FOR

Students of physical chemistry, educators in thermodynamics, and professionals seeking to deepen their understanding of energy relationships in chemical processes.

speny83
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Hi all, studying for a physical chemistry exam tomorrow morning and I'm getting really confused. I am hoping somebody has an easy to understand explanation of How a lot of this stuff works.

specifically the relationships between ΔH, ΔU, q & W and constan P,V & T
i.e. if P is constant how these relate VS If T is constant.

I understand the derivations of Heat transfer for constant P=constant and V= constant; as well as Wrev and wirr

also, I know the ΔU=w+q and dH=dU+d(pv)...is this last one the trick to finding U and H for given process?


I guess i don't really have a question, just pumping so much stuff into my head its all spinning around in circles and hoping someone can provide a couple statements that get me back on track.

Maybe a good place to start is if you could clearly explain when/where/why Δ_=0 for some of the above, i think maybes that where i getting all mixed up.

As always I really appreciate you helpful folks on this forum! Thanks.
 
Last edited:
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It isn't clear precisely what this OP is asking.
 

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