When electromagnetic radiation of wavelength 300 nm falls on the surface of a metal, electrons are emitted with the kinetic energy of 1.68 105 J mol-1. What is the minimum energy needed to remove an electron from the metal? (h = 6.626 10-34 J s, c = 3 108 m s-1, NA = 6.022 1023 mol-1)
- 2.31 105 J mol-1
- 2.31 106 J mol-1
- 3.84 104 J mol-1
- 3.84 10-19 J mol-1
Answer
(1) 2.31 105 J mol-1
Solution
Energy of one mole of photons:
E = NA hc
= 6.022 1023 6.626 10-34 3 108300 10-9
= 6.022 1023 6.626 10-19
= 3.99 105 J mol-1
Minimum energy (work function) W0 = E - KE
= 3.99 105 - 1.68 105
= 2.31 105 J mol-1
Answer: (1)