Author: **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.