Why Do Substances Expand On Heating? Molecular Explanation

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SUMMARY

The discussion centers on the molecular explanation for the thermal expansion of substances. It is established that as temperature increases, the distance between particles also increases due to the interplay of electromagnetic attraction and repulsive forces, specifically the Pauli exclusion principle. The potential energy curve illustrates that the average atomic separation increases with rising energy levels, resulting in expansion. Understanding this molecular behavior is crucial for interpreting thermal expansion in various materials.

PREREQUISITES
  • Basic understanding of molecular forces, including electromagnetic attraction and repulsion.
  • Familiarity with the Pauli exclusion principle and its implications on atomic behavior.
  • Knowledge of potential energy curves and their significance in molecular interactions.
  • Concept of thermal energy and its effect on particle movement.
NEXT STEPS
  • Study the relationship between temperature and kinetic energy in particles.
  • Explore the concept of potential energy wells in more detail.
  • Investigate the effects of thermal expansion in different materials, such as metals and polymers.
  • Learn about advanced topics in statistical mechanics related to molecular interactions.
USEFUL FOR

This discussion is beneficial for physicists, materials scientists, and chemistry students who seek a deeper understanding of thermal expansion and molecular dynamics.

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.
 
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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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