U1-1-2 - Energy Calculations

Question 1

A photon carries quantised energy proportional to the frequency of radiation.

What does ‘quantised’ mean?

Answer 1

Can only have specific set values (not any random value).

Think height of each step on a staircase/note or coin values.

Question 2

What is h?

Answer 2

Planck’s constant

Question 3

What is L?

Answer 3

Avogadro’s constant

(no. of particles in 1 mole of a substance)

Also denoted as N_A

Question 4

‘Calculate the energy, in kJ mol⁻¹, associated with a wavelength of 671 nm.’

What conversion must be done before the calculation?

Answer 4

671 nm must be converted into m (671 × 10^–9)

This is to match speed of light units, m s^–1.

Question 6

‘Calculate the wavelength, in nm, associated with energy of 280 kJ mol⁻¹.’

What conversion must be done before the calculation?

Answer 6

280 kJ mol⁻¹ must be converted into J mol⁻¹ (280 × 10³)

This is to match Planck constant units, J s.