Question

It takes 486.0 kJ/mol to convert sodium atoms to Na+ ions. Sodium atoms absorb and emit light of wavelengths 589.6 and 590.0 nm. Calculate the energy of the 590.0 nm light in kilojoules per mole.

Answer 1

We first calculate the energy contained in one photon of this light using Planck's equation:

E = hc/λ

E = 6.63 x 10⁻³⁴ x 3 x 10⁸ / 590 x 10⁻⁹
E = 3.37 x 10⁻²² kJ/photon

Now, one mole of atoms will excite one mole of photons. This means that 6.02 x 10²³ photons will be excited

(3.37 x 10⁻²² kJ/photon) x (6.02 x 10²³ photons / mol)

The energy released will be 202.87 kJ/mol