By using photons of specific wavelengths, die mists can dissociate gaseous HI to

Question

By using photons of specific wavelengths, die mists can dissociate gaseous HI to produce H atoms with certain speeds. When HI dissociates, the H atoms move away rapidly, whereas the heavier I atoms move more slowly, (a) If a photon of 254 nm is used, what is the excess energy (in J) over that needed for dissociation? (b) If this excess energy is carried away by the 11 atom as kinetic energy, what is its speed (in m/s)? (Bond energy of H- I is 295 kJ/mol.) Enter your answers in scientific notation. times 10 (select) J times 10 (select) m/s

Explanation / Answer

Energy of the photon of 234 nm will be

E = 1240 / 234 eV = 5.3 eV = 8.5 E-19 J/photon

Conisdering one photon interacts with one molecule

Dissocialtion enregy = 295000/6.23E23 = 4.73E-19 J/ molecule

Hence excess eerngy = 8.5 - 4.73 = 3.76 E-19 J

We know that Kinetic energy is given as

E = 1/2 mv^2

3.76E-19 = .5 * 1.6E-27 v^2

v =2.16 E4 m/s

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