Heat -> Molecular vibration

Can anyone help with the following - which I have been musing about for some time.
mThe general idea is that when heat is applied to a substance the molecules / atoms in that substance vibrate more and more (until the bonds in the molecule break). OK - so can anyone help with the following.

1. What is the actual carrier of energy (of say a flame) to the atoms.
2. Why should an atom vibrate as its energy increases?
3. I presume that IR radiation is the normal mechanism for atoms to lose this energy?

Can anyone add to this?

Thanks
 

DrClaude

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1. What is the actual carrier of energy (of say a flame) to the atoms.
A flame is not energy, it's made up of hot molecules. The main way in which energy is transfered is through collisions between molecules. Radiative transfer can also be important.

2. Why should an atom vibrate as its energy increases?
Using the simple classical picture of a molecule being little balls (atoms) connected by springs, you can imagine what happens when a molecule hits another one.

3. I presume that IR radiation is the normal mechanism for atoms to lose this energy?
Atoms don't emit or absorb in the IR part of the spectrum. Molecules do, but some barely (the main components of air, N2 and O2, are not active in the IR). Again, collisions are often the main mechanism by which heat is transferred.
 

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