Properties of light

Here are some important relationships:

E = hν E = hc/λ c = λν
c = 2.998 x 108 m/s h = 6.626 x 10-34 J s

What is the frequency (ν) of light with a wavelength of 488 nm?
6.14 x 1014 s-1 6.14 x 10-14 s-1 1.63 x 10-15 s-1 3.07 x 1014 s-1
This was easily calculated using ν = c/λ.

What is the energy (E) of a single photon of light with a wavelength of 488 nm?
20492 cm-1 4.07 x 10-19 J 245 kJ/mol 1.64 x 10-18 J
This one is calculated using E = hν or E = hc/λ.

What is the energy (E) of a mole of photons of light with a wavelength of 488 nm?
20492 cm-1 4.07 x 10-19 J 245 kJ/mol 1.64 x 10-18 J
Since the energy of one photon is given by E = hc/λ, the nergy of a mole of photons is given by E = NAhc/λ (Where NA is Avogadro's number.)

The first ionization potential of sodium is 495 kJ/mol. What is the maximum wavelength of light that will produce photoelectrons from sodium?
363 nm 484 nm 121 nm 242 nm
Since λ = hc/E,
          (6.626 x 10-34 J s)(2.998 x 108 m/s)    6.022 x 1023     kJ     109 nm
      λ = ------------------------------------ * ------------ * ------ * ------
                     495 kJ/mol                      mol        1000 J     m
      


Back to the
Chem 1102 page?

Patrick E. Fleming
California State University, East Bay
patrick.fleming@csueastbay.edu