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 $3.98\times 10^{-19}J$

Explanation:

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

$E=\frac{hc}{\lambda}$

where,

h = Planck's constant = $6.625\times 10^{-34}J.s$

c = speed of light = $3\times 10^8m/s$

$\lambda$ = wavelength = 500 nm = $500\times 10^{-9}m=5\times 10^{-7}m$    (Conversion factor: $1m=10^9nm$  )

Putting values in above equation, we get:

$E=\frac{6.625\times 10^{-34}J.s\times 3\times 10^8m/s}{5\times 10^{-7}m}\\\\E=3.98\times 10^{-19}J$

Hence, the value of energy change is $3.98\times 10^{-19}J$