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Vapour
Vapour
density is the density of a vapour in relation to that of hydrogen. It may be defined as mass of a certain volume of a substance divided by mass of same volume of hydrogen. vapour density = mass of n molecules of gas / mass of n molecules of hydrogen. Thus: vapour density = molar mass of gas / molar mass of H2 vapour density = molar mass of gas / 2.016 vapour density = ~½ × molar mass (and thus: molar mass = ~2 × vapour density) For example, vapour density of mixture of NO2 and N2O4 is 38. 3. Vapour
Vapour
density is a unitless quantity. Alternative definition[edit] In many web sources, particularly in relation to safety considerations at commercial and industrial facilities in the U.S., vapour density is defined with respect to air, not hydrogen.[1] Air is given a vapour density of one. For this use, air has a molecular weight of 28.97 atomic mass units, and all other gas and vapour molecular weights are divided by this number to derive their vapour density.[2] For example, acetone has a vapour density of 2[3] in relation to air. That means acetone vapour is twice as heavy as air. This can be seen by dividing the molecular weight of Acetone, 58.1[4] by that of air, 28.97, which equals 2. With this definition, the vapour density would indicate whether a gas is denser (greater than one) or less dense (less than one) than air. The density has implications for container storage and personnel safety—if a container can release a dense gas, its vapour could sink and, if flammable, collect until it is at a concentration sufficient for ignition. Even if not flammable, it could collect in the lower floor or level of a confined space and displace air, possibly presenting an asphyxiation hazard to individuals entering the lower part of that space. See also[edit]

Relative density
Relative density
(also known as specific gravity) Victor Meyer apparatus

References[edit]

^ MSDS Glossary of Terms – Vapor Density. Msdsonline.com. Retrieved on 2012-02-09. ^ HazMat Math: Calculating Vapor Density. Firenuggets.com. Retrieved on 2012-02-09. ^ MSDS: Acetone. Hazard.com (1998-04-21). Retrieved on 2012-02-09. ^ NIOSH Pocket Guide: Acetone. Cdc.gov. Retrieved on

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