Re: liquid nitrogen

In article <Pine.LNX.4.50.0604131425340.27460-100000@localhost>, Timo Nieminen <timo@xxxxxxxxxxxxxxxxx> writes:
On Thu, 13 Apr 2006, Dave Lister wrote:

jimp@xxxxxxxxxxxxxxxxxxxx wrote in news:ovt0h3-sq2.ln1@xxxxxxxxxxxxxxxx:

Dave Lister <retsildivad33@xxxxxxxxxxx> wrote:

It seems there is a large amount of potential energy in a closed
flask of liquid nitrogen. If just a small amount of heat is added, it
will change state and volume explosively.

How is this energy quantified and where is it stored?

If I put a closed flask of water into a 800 F oven, it will change
state and volume explosively.

Where does the energy come from?

The amount of energy seems to be a couple orders of magnitude different in
the two cases, yet the explosions are much the same.

Actually, in this case the energy required _is_ an order of magnitude
different. The latent heats of vaporisation of water and nitrogen are
about 2MJ/kg and 0.2MJ/kg.

But, anyway, assuming that you had 1 kg of liquid nitrogen, you'd still
need to add 200kJ of energy to get it to change phase. You call 200kJ
"just a small amount of heat"?

Just to provide a reference point, this amount of energy is about
equivalent to what's present in about 50g of TNT.

Perhaps you're thinking that the temperature only needs to rise a little
to get the phase change? Maybe so, but it takes a _lot_ of energy to get
that little temperature rise. Google "latent heat".

Mati Meron | "When you argue with a fool,
meron@xxxxxxxxxxxxxxxxx | chances are he is doing just the same"
.

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