# In a container, 77.3 atm SiF4 are mixed with 33.9 atm of O2. What are the mole fractions of each component?

Please explain to me how to do mole fraction calculations!!

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• There's nothing different about mole fractions and any other fractions.

In this particular case atmospheres are proportional to moles, so you can work in atm.

The total number of atmospheres is 77.3 atm + 33.9 atm = 111.2 atm.

The fraction of SiF4 is 77.3 / 111.2 = 0.695

You can leave it that way and say 0.695 is the mole fraction (or the fraction of pressure) but it's more common to convert it to a percentage: 69.5% SiF4

Then the shortcut for the other component is:

100% - 69.5% = 30.5% O2

But if you need to go the long way around:

33.9 / 111.2 = 0.305 = 30.5% O2

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• Assuming that both gases were originally at the same temperature and that the temperature is constant, mole fractions will be equal to the partial pressures of the two gases in the mixture.

Mole fraction SiF4 = 77.3 / (77.3 + 33.9) = 0.695

Mole fraction O2 = 33.9 / (77.3 + 33.9) = 0.305

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