[yor_on]

Now you're ever so happily moving into Terra incognito From how to define the 'energy' in solids and gas, in fact everything that is made out of particles/matter, too what 'energy' really, and I do mean really, is?

That one is interesting indeed. A photon is probably the closest definition of 'pure energy' as it is mass less, intrinsically time less, as well as not really being 'here' as it has no discernible 'size'.

Then you can also define 'energy' as a outcome of interactions where some of that 'energy' involved is gained in a transformation, by some particle or other, as 'usable energy', and some is 'lost' to SpaceTime as 'unusable energy'.

And in that motto 'energy' becomes a description of interactions, not existing on its own. In QM you have the quantum foam existing everywhere though, and that might also be used as a description.

[JP]

Temperature is a direct measure of the average kinetic energy of your gas,

Does this only apply to gases, or to liquids as well.How about the molecules vibrating in solids?

Gases are the easiest to think about since the gas molecules bounce about pretty freely in space.  In liquids and solids they're more confined, but the basic idea still holds: things vibrate faster when hot and if you bring a hot object in contact with a cold object, the collisions between vibrating particles will transfer heat energy until they're all vibrating at roughly the same rate.

Are you saying that the single, frozen, molecule will start moving about and eventually bounce off the container walls(assuming it's smooth walled)? Where does the force come from to start the motion?

In reality, nothing can ever be frozen.  No matter how much energy you take out of that molecule, it will still be vibrating slightly.  This is just a result of how things behave on tiny scales (quantum mechanics).  If the container walls are hot and the molecule is cooled down to almost motionless, it will take a long time, but eventually it will hit a wall and then it will gain energy--it will move faster, hit another wall, gain more energy, etc. 

Also, as CZARCAR said objects emit photons just because of their vibrations.  The hotter they are, the more photons they tend to emit--this is why really hot iron glows red, for example.  If you heat up the walls of your box, it will be emitting photons and some of these will hit your gas molecule and give it energy. 

[CZARCAR]

4get the N2 & use He to simplify. Cold He is placed in hot vacumn chamber, photons hit & electrons jump to higher shells. The He expands spatially? Bombarded with enough photons, will the electrons break free from the outermost shell & result in a freed electron & the He become + charged as a result of losing 1 electron?

[JP]

4get the N2 & use He to simplify. Cold He is placed in hot vacumn chamber, photons hit & electrons jump to higher shells. The He expands spatially? Bombarded with enough photons, will the electrons break free from the outermost shell & result in a freed electron & the He become + charged as a result of losing 1 electron?

Yeah, this will happen eventually.

[CZARCAR]

4get the N2 & use He to simplify. Cold He is placed in hot vacumn chamber, photons hit & electrons jump to higher shells. The He expands spatially? Bombarded with enough photons, will the electrons break free from the outermost shell & result in a freed electron & the He become + charged as a result of losing 1 electron?

Yeah, this will happen eventually.

has it been proven experimentally or theoretically?   just curious

[JP]

I don't think anyone has done the test of a single molecule in a hot box.  It would be incredibly hard to do.

But people have experimentally tested black body radiation, and they have experimentally tested the reaction of atoms and molecules to being hit with light, so it's pretty clear what would happen to a single atom struck by black body radiation.

[Johann Mahne]

Thanks everyone for all the replies.
They have improved my understanding somewhat,although more questions seem to crop up, but i'll ask them on another post.
Cheers
Johann