Question

Strontium has a visible line in its spectrum at 631.3 nm. What is its energy in kJ/mol?

Your Answer:

Question 4 options:

Answer	units

Retinal damage can be caused by light between 445 nm and 470 nm. What is the energy in kJ/mol of photons with a wavelength of 464.0 nm?

Your Answer:

Question 5 options:

Answer	units

Answer 1

Energy of a photon with wavelength λ (in m) can be determined by the formula below:

E = hc/ λ

Where, E = Energy of a photon (J)

            h = Planck’s constant (6.626*10^-34 J.s)

            c = speed of light in vacuum (3*10⁸ m.s^-1)

            λ = Wavelength of photon (m)

Part 1:

Given λ = 631.3 nm

            = 631.3*10^-9 m   (1 nm = 10^-9 m)

Energy of single photon of wavelength 631.3 nm

= (6.626*10^-34 J.s * 3*10⁸ m.s^-1)/( 631.3*10^-9 m)

= 3.149*10^-19 J

So, Energy of 1 mol of photon of wavelength 631.3 nm

= (3.149*10^-19 J/photon) * (6.022*10²³ photon/mol)

= 189632.78 J/mol

= 189.6 kJ/mol        (1 kJ=1000 J )

So the answer is 189.6 kJ/mol.

Part 2:

Given λ = 464.0 nm

            = 464.0*10^-9 m   (1 nm = 10^-9 m)

Energy of single photon of wavelength 631.3 nm

= (6.626*10^-34 J.s * 3*10⁸ m.s^-1)/( 464.0*10^-9 m)

= 4.284*10^-19 J

So, Energy of 1 mol of photon of wavelength 631.3 nm

= (4.284*10^-19 J/photon) * (6.022*10²³ photon/mol)

= 257982.48 J/mol

= 257.9 kJ/mol        (1 kJ=1000 J )

So the answer is 257.9 kJ/mol.