Question

A hydrogen-discharge lamp containing 0.01 moles of hydrogen molecules. When in operation, H2 is dissociated into H atoms before emitting a photon at 121 nm. How many joules of energy is released when each atom emits one single photon?

Answer 1

numer of H2 molecule = (6.022*10^23)*(number of mole of H2)
= (6.022*10^23)*0.01
= (6.022*10^21)

number of H atom = 2*(6.022*10^21)
= (12.044*10^23)
number of photon emitted = (12.044*10^23)

wavelength = 121 nm
= 121*10^-9 m
energy of each photon = (h*c)/(wavelength)
= (6.6*10^-34*3*10^8)/(121*10^-9)
= (16.4*10^-19) J

total energy emitted = (number of photon emitted)*(energy of each photon)
= (12.044*10^23)*(16.4*10^-19)
= (1.98*10^6) J

Answer : (1.98*10^6) J