By using photons of specific wavelengths, chemists can dis-sociate gaseous HI to produce H atoms with certain speeds.When HI dissociates, the H atoms move away rapidly, whereasthe heavier I atoms move more slowly. (a) What is the longestwavelength (in nm) that can dissociate a molecule of HI? (b) If aphoton of 254 nm is used, what is the excess energy (in J) overthat needed for dissociation? (c) If this excess energy is carriedaway by the H atom as kinetic energy, what is its speed (in m/s)?

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By using photons of specific wavelengths, chemists can dis-sociate gaseous HI to produce H atoms with certain speeds.When HI dissociates, the H atoms move away rapidly, whereasthe heavier I atoms move more slowly. (a) What is the longestwavelength (in nm) that can dissociate a molecule of HI? (b) If aphoton of 254 nm is used, what is the excess energy (in J) overthat needed for dissociation? (c) If this excess energy is carriedaway by the H atom as kinetic energy, what is its speed (in m/s)?

Expert Solution
Step 1

The bond energy of HI = 295 kJ/mol.

The energy of 1 molecule of HI using the Avogadro's number:

E (HI)molecule=295 ×103 J6.023×1023=48.979 ×10-20 J/molecule.

Step 2

a) Then, the maximum wavelength per molecule is:

λ =h cEλ =6.626×10-34 J.s ×3×108 m/s4.8979× 10-19J/molecule=4.058 ×10-7 m=405.8 nm

 

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