Question

A good vacuum pump on Earth can produce a vacuum with a pressure as low as 1.96 × 10-8 torr. How many molecules are present in each milliliter at a temperature of 23.0ºC?

Answer 1

At 1 atm = 760 Torr and 0^oC, 1 mole of any gas contains 6.02E23 particles of gas and occupies a volume of 22.4 Liters. This number of particles would be reduced by (1.96E-8/760)if at 0^C. At 23^oC = 296K the number of particles would be also be reduced by(273/296)because of temp expansion to the volume at 23^C. So, the number of Particles at 1.96E-8 Torr = (6.02E23/22.4)(1.96E-8/760)(273/296) particles => 6.39E11 particles (molecules).