Question

1. The Lennard-Jones 6-12 potential energy, which describes the potential energy between neutral gases, is u(r) = u0 h r0 r 12 − 2 r0 r 6 i , where r is the separation between atoms. For Ar r0 = 3.9 × 10−10 m and u0 = 1.6 × 10−21 J (according to D. V. Schroeder, An Introduction to Thermal Physics). (a) Roughly sketch the form of the potential energy as a function of r. On your diagram indicate the value of r and u at the minimum energy in terms of r0 and u0 (note: du dr = 0 at this point). Also indicate where the potential energy starts to become positive, and its behaviour as r → infinity.) AND Derive an expression for the force between the atoms as a function of r. On your diagram from (a) label the regions where the force is negative (attractive) between atoms, and where the force is positive (repulsive) between atoms

Answer 1