I Why is ##dQ = dH## still valid for chemical reaction (Callen)?

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The discussion centers on the validity of the equation dH = dQ in the context of chemical reactions, particularly as presented in Callen's work. It highlights that while Callen assumes constant mole numbers (dN_i = 0) to derive dH = dQ, this assumption does not hold in general for chemical reactions where mole numbers change. Participants debate the implications of irreversibility in chemical processes, noting that spontaneous reactions cannot be treated as quasistatic, which complicates the application of the first law of thermodynamics. The conversation emphasizes the need to consider the effects of entropy generation and the conditions under which dH can equal dQ. Ultimately, the discussion seeks clarity on reconciling these thermodynamic principles in the context of real chemical reactions.
  • #31
DrDu said:
Just to give some other examples: You could run a reaction far from equilibrium quasistatically if it requires some homogeneous catalyst and you are using very small concentrations of it. In case of enzymatic reactions, reactions will run very slowly at lower temperatures.
You could also run a reaction reversibly using a van't Hoff equilibrium box.
 
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  • #32
Chestermiller said:
You could also run a reaction reversibly using a van't Hoff equilibrium box.
Yes, but I understood that the question was whether you can run a non-equilibrium reaction quasistatically, not reversibly.
 
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