First step is to change temperature and pressure into SI units: 50 degree celcius = 50 + 273 = 323 degree kelvin 650 mmHg = 650/760 = 0.855 atm
Second step is to calculate the number of moles of N2 that can be found under the mentioned conditions using the rule: PV = nRT where: P is the pressure, V is the volume, n is the number of moles, R is the gas constant (= 0.08206) and T is the temperature. Substituting in the equation we get: 0.855 x 2.5 = n x 0.08206 x 323 n = 0.0806 moles
Third step is to get the number of molecules in 0.0806 moles by multiplying the number of moles by Avogadro's number: number of molecules = 0.0806 x 6.02 x 10^23 = 0.485212 x 10^23 molecule
