PROBLEMS FOR PRACTICE

1. When gaseous HI is irradiated with radiation of 2350 A wavelength, it is observed that 1.85 • 10*2 mole decomposes per 1000 cal of radiant energy absorbed. Calculate the quantum efficiency of the reaction
[Ans. 1.9]

2. A certain system absorbs 3.0 • 1016 quanta of light per second. On irradiation for 20 minutes,
0.002 mole of the reactant was found to have reacted. Calculate the quantum efficiency of the process.
[Ans. 0.669]

93. The quantum yield of light-induced chemical reactions (called photochemical reactions) measures the efficiency of the process. The quantum yield, ¢ is defined as: number of reaction events number of photons absorbed Suppose the quantum yield for the reaction CH3 – CH3 + X is =0.24. A cuvette con- taining a solution of CH X is irradiated with 280-nm light with a power of 885 mW for 10.0 minutes. Assuming total absorp- tion of the light by the sample, what is the maximum amount (in moles) of CH3X that breaks apart?

the quantum yield for CO production in the photolysis of gaseousacetone is unity for wavelengths between 250 and 320 nanometers.After 20 minutes of irradiation at 313 nm, 18.4 cm cubed of CO(measured at 1008 pascals and 22 ^oC ) is produced.calculate the number of photons absorbed, and the intensity in Js^-1.

94. A student is studying the photodissociation (dissociation with light) of 12 — 21. When a sample of I, is irradiated with a power of 255 mW at 590 nm for 35 seconds, 0.0256 mmol of I forms. Assuming complete absorption of the incident radiation, what is the quantum yield, 4, of the reaction? (See Problem 93 for definition of quantum yield.)