Partial Pressure vs Mole Fraction

[member232]

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What is the difference between partial pressure and mole fraction?

For example, a question states: At a low altitude with a low ambient temperature, what is true of atmospheric air?

Answer: It has a higher partial pressure of O2 (g), but the same mole fraction of O2 (g) as normal air.

If mole fraction is Moles [ O2] / Total Moles and partial pressure is [Ptotal] [Mole fraction], how is it that the number of moles of O2 stay constant, but the pressure due to O2 increases??

Thanks in advance!!

 

[Raiden2012]

Ptotal is higher at lower altitudes. So with same mole fraction, partial pressure is higher

 

[illinichief89]

there is more total pressure at a low altitude compared to a high altitude, so if the mole fraction of O2 is the same at both altitudes, then the partial pressure of O2 will be higher at a lower altitude because there is a larger total pressure there.

 

[member232]

definitely overthought this one, thanks!!