Question

a)For a photon of 9.75 cm-1, what is the corresponding frequency in GHz?

b)A lamp emits light of wavelength 612 nm.
What is the energy of this radiation in kJ mol^-1?

c)If a sample absorbs 28.3% of the light at a given wavelength,
what is the corresponding absorbance value?

Answer 1

(a) Given 1/ = 9.75 cm^-1  

For a photon frequency, = C / = 3x10¹⁰ cm.s^-1 x 9.75 cm^-1 = 2.925x10¹¹ s^-1 = 2.925x10¹¹ Hz

=  2.925x10¹¹ Hz x (10^-9 GHz / 1 Hz) = 292.5 GHz (answer)

(b): E = hc / = (6.626x10^-34 J.s x 3.0x10⁸ m.s^-1 ) / 612x10^-9 m = 3.25x10^-19 J / radiation

Hence energy radiated by N_A ( = 6.023x10²³) photons = (3.25x10^-19 J / radiation ) x 6.023x10²³ radiation / mol

= 195747.5 J/mol = 195.75 KJ/mol (answer)

(c): % of radiation absorbed = 28.3 %

Hence %age transmitted, T = 100 - 28.3 = 71.7 % = 0.717

A = log(1/T ) = - log(0.717) = 0.144