9 6 pts The energy required to remove one mole of electrons

9. (6 pts) The energy required to remove one mole of electrons from the surface of Li (s) is 280 kJ/mol. When light composed of photons with a certain energy hits the surface of Li (s), the electrons leaving the surface have a kinctic energy of 62 kJ/mol. What is the energy of a mole of the photons used to irradiate Li (s)? A) 309kJ/mol B) Less than 309 kJ/mol C) More than 342 kJ/mol D) 342 kJ/mol E) None of the above

Solution

Energy of mol of photon used to irradiate Li(s)=energy required to remove electrons+energy gained as kinetic energy by the electrons=280KJ/mol+62KJ/mol=342KJ/mol(D)

A part of the incident radiation is used up in extracting electrons from the Li surface ,but the remaining energy of the incident radiation isused up to increase the kinetic energy of the removed electrons.