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Asked by anon-267549 on 10 Nov 2020.
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Daisy Shearer answered on 10 Nov 2020:
The answer to this would change depending on your altitude because air gets less dense higher up in the atmosphere. It’s also impacted by factors like temperature and pressure. But to make things easy, let’s assume we’re at sea level. Under these conditions, the pressure is around 1×10^5 Pa and the temperature is around 288K (which is around 15 degrees celsius). We can use gas laws to work out how many moles of air we have: pV=nRT (p is the pressure in pascals, V is the volume, n is the number of moles, R is the gas constant which is 8.31, and T is the temperature in kelvin). Rearranging this, we get: n=pV/RT = ((1×10^5)x1)/(8.31×288) = 42mol (approximately). We can then find the number of molecules by multiplying the number of moles by the number of molecules in a mole (Avogadro’s number): 42 x (6.02×10^23) = 2.5×10^25 particles!
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Sam Geen answered on 11 Nov 2020:
In deep space between galaxies, there is sometimes only 1 particle in every cubic metre. There’s no real “air” in space, though – the chemistry of space is mostly hydrogen and helium, and other atoms only make up 1-2% of the gas. The Earth’s atmosphere is more complex because hydrogen and helium are so light that they can easily escape into space – this is why we have to be careful with our helium, because once it’s gone it’s hard to get back.
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