Posted by **mel** on Saturday, November 17, 2007 at 4:30pm.

Use the data in Table 5.4 to calculate the partial pressure of He in dry air assuming that the total pressure is 1.0 atm. Assuming a temperature of 21°C, calculate the number of He atoms per cubic centimeter.

atoms/cm3

.00000524 - atmospheric composition of airnear sea level for He(info from table)

not a clue

- dr. bob -
**DrBob222**, Saturday, November 17, 2007 at 5:35pm
What are the units here (for the composition of Helium at sea level)? percent? mols?

- dr. bob -
**mel**, Saturday, November 17, 2007 at 10:07pm
moles

- dr. bob -
**drwls**, Sunday, November 18, 2007 at 12:02am
In the Earth's atmosphere, the concentration of helium by volume (also called the "mole fraction") is 5.2 parts per million. At 1 atm and 21C, the molar density of air is

1 mole /24,100 cm^3. Multiple that by the mole fraction and Avogadro's number for the number of He atoms per cm^3.

I get 1.3*10^13.

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