Number of molecules: What is the number of molecules in a diatomic gas present in `1 L` flask at `0^(@) C` and under a pressure of `7.6xx10^(-19) mm Hg`?
Strategy : Express the pressure in atmosphers and use Eq.(1.10) to calculate the number of moles. Using Avoagdro's constant,find the number of molecules.

Explanation

Step 1: pressure
`= (7.6xx10^(-10) "mm Hg") (("1 cm Hg")/("10 mm Hg")) (("1 atm")/("76 cm Hg"))`
`= 10^(-12) "atm"`
`v = 1 L, R = 0.0821 "L atm K"^(-1) mol^(-1), T = 273 K`
using Eqs., we have,
`n = (PV)/(RT) = ((10^(-12) "atm") (1 L))/((0.821 "L atm K"^(1) mol^(-1)) (273K ))`
`= 0.44xx10^(-12) mol` of diameter gas
Step 2 : Accroding to Eq. (1.8),m we have
Number of molecules
= (Number of moles) `xx` (Avogadro's constant)
`= (0.44xx10^(-12) "mol")(6.022xx10^(23) ("molecules")/("mol"))`
`= 2.6xx10^(10)` molecules