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Name: Bhola
Status: N/A
Grade: 9-12
Location: N/A
Country: N/A
Date: 9/25/2005


Question:
While I was learning about carbon dioxide, it was written in my book that it is the heaviest gas. What is the reason behind being heavy? Does heaviness have some relation with molecular weight?


Replies:
Whether a substance is a gas, liquid, or solid depends on the temperature as well as the molecular weight so which gas is "heaviest" depends upon the temperature, pressure and what composition restrictions you want to place on the class of substances. The molar density of a gas is given fairly accurately by the ideal gas law: PV=m/MRT, where R=0.082 liter-atm/mol kelvin, m = the mass, M = molecular weight, and T is in kelvins, with P in atmospheres and V in liters. Of the permanent stable ELEMENTS at room temperature xenon, Xe, is the most dense with a molecular weight of 131.293. Radon, Rn is more dense with an approximate molecular weight of 222 but it is radioactive. So it is a little misleading to even ask the question which gas is "heaviest" without specifying what I discussed above.

Vince Calder



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