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Energy Storage

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Energy Storage

Unread postAuthor: shud_b_rite » Thu Apr 26, 2007 4:22 am

I have 2 questions.

1.Say that I have a tank with a volume of 1000 cu/cm and it was pressurized to 100psi with air at room temperature. Roughly how much energy (im talking joules/kilo joules) is stored in it? I have done research on this but the calculations were very complicated and confusing, I just need a little help.

2.I have myself 1,000cu/cm of liquid nitrogen at -190 something degrees celsius. The liquid nitrogen was placed into a 10,000 cu/cm container and heated to room temperature so all of the liquid evaporated. How much pressure would be in the container? Again I have researched this but have not found anything to do with pressure on this subject.

Can anyone help me with this?
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Unread postAuthor: ShowNoMercy » Thu Apr 26, 2007 5:41 am

You could try using the equation for Kinetic tranlational energy, which is K = (3/2)kT and that would put the energy of the first gas at around, 6.21 E-22 asssuming a 30 degree celssious room temperatuure. And then for your second question I would suggest using heat equations with a change in matter thrown in there too. Its to early for those kind of equations though.
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Unread postAuthor: jimmy101 » Thu Apr 26, 2007 11:11 am

For your second question this is where you use the ideal gas law;
PV=nRT
where
P=pressure,
V=volume,
n=number of moles of gas,
R=gas constant and
T=absolute temperature.

You want to calculate the final pressure so rearrange the eq to;
P=nRT/V

For n you'll need to know the weight of the gas and its molecular weight. You'll need to look up the density of liquid nitrogen in order to calculate the weight of the nitrogen from its volume. Nitrogen's molecular weight is 28g/mol. (Ntirogen is diatomic, N<sub>2</sub>, so the molecular weight is twice the atomic weight of nitrogen.)
n=(volume nitrogen)(density nitrogen)/(molecular weight of nitrogen)
Be careful of the units, they need to cancel out correctly. If the density is in g/ml then the volume need to be in ml as well.

R= 0.08206 L·atm/K/mol (See the Wiki <a href="http://en.wikipedia.org/wiki/Gas_constant">Gas Constant</a> page if you need R in other units)

T= temperature in degrees Kelvin, 72F = 300K

V= 10,000cm<sup>3</sup> (not cu/cm) = 10L

Plug the values into the equation. Include the units for each of the values. Cancel any units that you can. Calculate the numbers. Add the remaining units to the number. Check that the remaining units are what you want. In this case, the remaining units should be pressure (or force/area).

Edit: Fixed bad wiki link.
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Unread postAuthor: ShowNoMercy » Thu Apr 26, 2007 12:00 pm

Wouldnt you not be able to use that formula because it changes state?
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Unread postAuthor: paaiyan » Thu Apr 26, 2007 1:04 pm

You can use the formula to calculate the pressure of the gas after it has changed phase. You get the number of moles of nitrogen, and then use that to determine the pressure at your given volume and temperature. Then you can use that pressure to calculate potential energy.
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Unread postAuthor: shud_b_rite » Fri Apr 27, 2007 12:45 am

Oh yes, thanks everyone. My chemistry and physics classes are coming back to me now. Thanks
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