Why Do Substances Expand On Heating? Molecular Explanation

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    Expansion Heating
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Discussion Overview

The discussion centers on the molecular explanation for why substances expand when heated, exploring the underlying mechanisms and interpretations of thermal expansion at the atomic level.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant seeks an understandable molecular account of thermal expansion.
  • Another participant expresses confusion regarding the potential energy curve and its relation to thermal expansion, indicating a need for clarification on the explanation provided in a referenced book.
  • A different participant proposes that the shape of the pair potential curve influences average atomic separation as temperature increases, attributing this to the balance of electromagnetic attraction and repulsive forces due to Pauli exclusion.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as there is confusion about the explanations provided and differing interpretations of the potential energy curve's implications.

Contextual Notes

Limitations include the need for clearer definitions of terms such as "pair potential" and "average atomic separation," as well as unresolved questions about the relationship between energy and atomic spacing.

Pranav Jha
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Why do substances expand on heating? Please give an understandable molecular account of the process of expansion.
 
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Mapes said:
Try http://books.google.com/books?id=rVVW22pnzhoC&pg=PA397".

I don't think I understand the concept. The potential curve got me thinking but still couldn't convince me about the thermal expansion. The book says that when temperature increases, the distance between the particles increases based on the PE curve. I think that was just reiterating the original question. So, I need your help to interpret the explanation in the book.
 
Last edited by a moderator:
Are you asking why the pair potential has the certain shape so that average atomic separation increases with increasing energy? Fundamentally, it's because atoms are electromagnetically attracted to each other, but a very strong repulsive force (arising from Pauli exclusion) acts at short distances. The sum of these two forces creates an asymmetric energy well that determines average atomic spacing.
 

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