# Physics Help Please?

a) Find the number of moles in 3.74 m3 of an ideal gas at 20.0°C and atmospheric pressure.

b) For air, Avogadro's number of molecules has mass 28.9 g. Calculate the mass of 3.74 m3 of air.

c) State how this result compares with the tabulated density of air at 20.0°C.

### 1 Answer

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- BrentLv 63 years agoFavorite Answer
a) The molar volume of any gas at STP (0°C, 1 atm) is 22.4 L. We adjust this value to 20.0°C:

22.4 L/mol * 293.15 K / 273.15 K = 24.04 L/mol

For 3.74 m³, we find the number of moles:

n = 3.74 m³ * 1000 L/m³ * 1 mol / 24.04 L = 156 mol

b) "Avagadro's number of molecules" means one mole.

Mass, m = 155.57 mol * 28.9 g/mol = 4496 g or 4.50 kg (3 significant figures)

c) Density = mass/volume = 4.496 kg / 3.74 m³ = 1.20 kg/m³

Wikipedia says 1.2041 kg/m³. They are in agreement.

Source(s): https://en.wikipedia.org/wiki/Density_of_air

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Thank you very much and great job on the explaining it.