1.
We nned to mention the initial pressure
2.
use:
P*V=n*R*T
3*10^-3*1 = n*0.0821*251
n=1.456*10^-4 mol
number of molecules = number of moles * Avogadro's
number
                                            Â
= 1.456*10^-4 mol * (6.022*10^23)
                                             Â
= 8.8*10^19 molecules
Answer: 8.8*10^19 molecules
3.
volume of CO2 = 0.04% of 3 L = 1.2*10^-3 L
use :
P*V=n*R*T
1*(1.2*10^-3)= n*0.0821*(273+29)
n = 4.84*10^-5 mol
number of molecules = number of moles * Avogadro's
number
                                            Â
= 4.84*10^-5 * (6.022*10^23)
                                             Â
= 2.9*10^19 molecules
Answer: 2.9*10^19 molecules
