How does the Enthelpy change tell us about the stability of the product?

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Discussion Overview

The discussion centers on the relationship between enthalpy change and the stability of chemical products, particularly in the context of constant pressure conditions. Participants explore the implications of negative enthalpy changes and question the adequacy of this measure for determining product stability, while also referencing instructional materials and videos.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that a negative enthalpy change indicates product stability, but express confusion over this claim, questioning the role of work in the internal energy equation.
  • Others seek references to support the assertion that negative enthalpy change correlates with stability, indicating a desire for authoritative backing.
  • A participant critiques a referenced video for its imprecision, arguing that it fails to adequately explain the heat of formation and incorrectly describes the system as adiabatic.
  • This participant emphasizes that a decrease in Gibbs free energy is a more appropriate criterion for assessing stability than enthalpy change alone.

Areas of Agreement / Disagreement

Participants do not reach a consensus; there are competing views regarding the relationship between enthalpy change and product stability, with some supporting the negative enthalpy criterion and others challenging it in favor of Gibbs free energy considerations.

Contextual Notes

Participants highlight limitations in the explanations provided in instructional materials, noting that assumptions about heat and work are not fully addressed. The discussion reflects uncertainty about the definitions and implications of enthalpy and Gibbs free energy in the context of chemical stability.

Frigus
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At constant pressure Enthalpy change is equal to heat exchange and we say that "if Enthalpy Change is negative then product formed is stable",
I am not able to make sense of this statement as change in Enthalpy tells us only about heat exchange but internal energy is function of both Work and Heat.
what if work done on the system is more than the heat released?
 
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Hemant said:
At constant pressure Enthalpy change is equal to heat exchange and we say that "if Enthalpy Change is negative then product formed is stable",
I am not able to make sense of this statement as change in Enthalpy tells us only about heat exchange but internal energy is function of both Work and Heat.
what if work done on the system is more than the heat released?
Please provide a reference for that statement.
 
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Chestermiller said:
Please provide a reference for that statement.

It is also Written it in my notes which are recited by my teacher.
 
Hemant said:

It is also Written it in my notes which are recited by my teacher.

With all due respect to your teacher and to this video, they are incorrect.

I have very big problems with this video, because it is extremely imprecise with its explanation (which demands being precise). For example, it does not say that the heat of formation is the amount of heat that has to be added to hold the system at the same temperature as it was initially. Clearly, this is pretty important, but it is omitted. If fact, at some point he even says that the system is adiabatic (which it is not).

Enthalpy decrease is not a criterion for stability of the products relative to the reactants. The correct criterion is a decrease in Gibbs free energy between reactants at the specified temperature and pressure and products at the same temperature and pressure. Even this is a rough rule of thumb.

In my view, this video should never be shown to students because of its low quality. Shame on the speaker.
 
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