Question

How many air molecules are present in 1cm³ of air ( 80% N₂ and 20% O₂ by number) at 1 atm and 298k?

Answer 1

We know that ideal gas equation is PV = nRT

Where

T = Temperature = 298 K

P = pressure = 1 atm

n = No . of moles = ?

R = gas constant = 0.0821 L atm / mol - K

V= Volume of the gas = 1 cm³ = 1 mL = 10^-3 L

Plug the values we get n = ( PV) / (RT)

                                    = 4.09x10^-5 moles

we know that 1 mole of any compound contains avagadro number(6.023x10²³) molecules

4.09x10^-5 moles contains 4.09x10^-5 x6.023x10²³ = 2.46x10¹⁹ molecules of air