Question

An electron returns from an excited state to its ground state, emitting a photon at λ = 500 nm. What would be the magnitude of the energy change if one mole of these photons were emitted? (Note: h = 6.626 × 10-34 J·s)

A. 3.98 × 10-21 J
B. 3.98 × 10-19 J
C. 2.39 × 103 J
D. 2.39 × 105 J

Answer 1

Answer: The value of energy change is
`3.98* 10^(-19)J`

Step-by-step explanation:

To calculate the energy of one photon, we use Planck's equation, which is:

`E=(hc)/(\lambda)`

where,

h = Planck's constant =
`6.625* 10^(-34)J.s`

c = speed of light =
`3* 10^8m/s`

`\lambda` = wavelength = 500 nm =
`500* 10^(-9)m=5* 10^(-7)m` (Conversion factor:
`1m=10^9nm` )

Putting values in above equation, we get:

`E=(6.625* 10^(-34)J.s* 3* 10^8m/s)/(5* 10^(-7)m)\\\\E=3.98* 10^(-19)J`

Hence, the value of energy change is
`3.98* 10^(-19)J`