Chemistry

Transporting Helium



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Helium is the second element of the periodic table in the noble gas family. It is also known for being inert, which means it generally does not react with any of the elements. Helium also has the distinctive characteristic of an extremely low boiling temperature of 4.22 K ( -452.07 degrees Fahrenheit). Therefore, it would be unrealistic in most cases to lower the temperature of helium enough to liquify it and transport it, even though that would give the greatest amount of helium in a fixed volume. Cost efficiently, the manufactures must find a method of packing the most amount of helium in a container. The problem basically reduces to the gas law, PV = nRT. (P- pressure, V-volume, R- rate constant, T- temperature) With n representing the number of moles (one mole is about 6.023 X 10^23 atoms) of helium, it is more profitable to have a higher n. As more moles of helium are added to a solid container (meaning constant volume) with generally constant temperature, the pressure will increase in relation to the number of moles.

After filling a tank with helium, there now exists a difference in pressures between the isolated tank environment and the outside atmosphere of approximately one atmosphere. If there is an opening or leak in a pressurized tank, a gas will have a natural tendency to flow from high pressure to low pressure to establish equilibrium between the two environments. While valves in the opening of helium tanks allow people to release controlled amounts of helium, a hole in the tank will cause a rapid release of helium. Because of helium's relatively much smaller size to most molecules, such as the nitrogen, oxygen, argon, and carbon dioxide which comprise the air, helium travels very quickly out of the tank, so any hope of repairing a punctured tank before it is all released it futile. A temporary patch would also be hard to place, because of the high pressure environment. Therefore smaller tanks are more reasonable. Furthermore, a larger tank at the same pressure as a smaller one is more dangerous, since there is more volume attempting to equalize quickly, so it could burst through more places in tank or enlarge the current one which poses more of a safety hazard for any one handling the tank.

Therefore, small, pressurized containers allow for a safe, and effective method of transporting helium to its various destinations. So next time there is a birthday party with the fun of helium balloons, remember why the helium is sitting there in the tank.

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