1.

Estimate the total number of air molecules (inclusive of oxygen, nitrogen, water vapour and other constituents) in a room of capacity 25.0 m3 at a temperature of 27°C and 1 atm pressure.

Answer»

Here, p = 1 atm = 1 x 1.01 x 105 Pa

V = 25 m3

T = 27°C = 27 + 273 = 300 K

and R = 8.31 J mol-1 K-1

Now pV = uRT

⇒ u = pV/RT = {1.01 x 105 x 25}/{831 x 300} = 1.013 x 103 moles

Now, one mole of a gas contains = 6.023 x 1023 molecules

∴ 1.013 x 103 moles would contain

= 6.023 x 1023 1.013 x 103 = 6.10 x 1026 molecules



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