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In a message dated 2/10/99 4:34:10 PM Central Standard Time, Ben.Carbery@tv*.co*.au* writes: << We must remember that there are two common ways of expressing the proportion of a particular gas in a mixture - by volume and by mass. I have always assumed that the commonly stated ratios of air, i.e. roughly 20% oxygen/ 80% nitrogen were expressions by volume. (I could be wrong however). In this case we cannot calculate the mass of EanX mixtures using these ratios. >> Yes, the common way of measuring gas is by volume. It does not follow, however, that one cannot calculate mass using these ratios. We express the Fraction of a gas in a mix as its percent by volume or partial pressure. They are the same (Check Henry's Law - It states that the fractional volume of a gas in a mix of gasses is proportional to its partial pressure.). Remember the universal gas law: PV=NRT Rearrange the terms: N=PV/RT N is the number of moles of gas. A mole is the mass of the atomic weight of the gas in grams. P is the absolute pressure of the gas (or partial pressure in this case). V is the volume. R is the universal gas constant. T is the absolute temperature. It should be quite apparent from this that the mass of a gas is, indeed, proportional to its fraction in the mix. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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