Why Do Substances Expand On Heating? Molecular Explanation

[Pranav Jha]

Why do substances expand on heating? Please give an understandable molecular account of the process of expansion.

 

[Mapes]

Try http://books.google.com/books?id=rVVW22pnzhoC&pg=PA397".

 

[Pranav Jha]

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.

 

[Mapes]

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.