posted by mel .
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.
.00000524 - atmospheric composition of airnear sea level for He(info from table)
not a clue
What are the units here (for the composition of Helium at sea level)? percent? mols?
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.