Question

One of the lines in the spectrum of a mercury vapor lamp has a wave length of 254nm. What is the energy, in kj/mol, of this electro magnetic radiation.

The work I have done:

(6.626 x 10^-34 x 3.0 x 10^8) all divided by (254 x 10^-9.)

The answer I calculated is 7.82 x 10^-19. The actual answer is 471 Kj/mol.

Can someone please explain to me where I have gone wrong?

Answer 1

You just didn't go far enough. What you have is correct and the answer of 7.82 x 10^-19 joules is the energy PER PHOTON. The question asks for kJ/mol; therefore, multiply your answer by 6.022 x 10^23 to convert to moles, then divide by 1000 to convert to kJ/mol. I obtain 471.

Answer 2

Thank you very much.