**PURPOSE: **To experimentally determine the diameter of the nitrogen molecule and to determine the order of magnitude of the mean free path of nitrogen gas molecules at STP.

**DESCRIPTION: **Using the pan balance pour 700 cm^3 of liquid nitrogen and demonstrate that it has a mass of 563 grams. For liquid nitrogen the volume per molecule can then be determined to be

Vol/Mol=700 cm^3/[(563g)/(28g/mole)(1mole/6.0x10^23molecules)]=5.8x10^-23cm^3.

Assume molecule is a cube, so d = 4x10^-8 cm.

Volume of molecule @ STP = 22.4x10^-20 cm^3 / 6.0 x 10^23 = 3.7x10^-20 cm^3

Mean free path = V/d^2 = 3.7x10-20 cm^3 / (4x10^-8 cm)^2 = 2x10^-5 cm.

**SUGGESTIONS: **

**REFERENCES: ** (PIRA
unavailable.)
See Demonstration Reference File for further information.

**EQUIPMENT: **two dewars, liquid nitrogen, pan balance.

**SETUP TIME: **5 min.