Question

By using photons of specific wavelengths, chemists can dissociate gaseous HI to produce H atoms with accurately known speeds. When HI dissociates, the H atoms move away rapidly, whereas the relatively heavy I atoms move little. Use Table 9.2 in your textbook to answer the following questions: (a) What is the longest wavelength (in nm) that can dissociate a molecule of HI? 4.9) 406 nm (b) If a photon of 226 nm is used, what is the excess energy (in )) over that needed for the dissociation? 4.9 3.90E.19x Your response differs significantly from the correct answer. Rework your solution from the beginning and check each step carefully. ] (c) If all of this excess energy is carried away by the H atom as kinetic energy, what is its speed (in m/s)? m/s Bond Energy Bond Energy Bond Energy Average Bond Energies (kJ/mol) Bond Energy Single Bonds H-H H-F H-CI H-Br H-I 323 391 160 347 266 226 209 201 327 N-H N-N N-P N-O N-F N-CI N-Br N-1 Si-H. Si-Si Si-O Si-S Si-F Si-CI Si-Br Si-I S-H S-S S-F S-CI S-Br S-1 226 565 295 271 218 -170 200 TIL 381 413 310 347 159 234 159 301 305 467 320 212 358 351 C-H C-C C-Si C-N C-o C-P C-s C-F C-CI C-Br C-1 264 204 213 200 490 243 259 F- F F-CI F-Br F-1 CI-CI CI-Br CI-1 Br-Br Br- 1-1 P- H P-Si P-P P-F P-CI P-Br P- I 265 0-H 0-P 0-0 0-S O-F 0-CI 0-Br 0-1 215 453 331 193 339 276 190 203 234 234 272 184 175 151 Multiple Bonds CEC CEN C=0 614 N=N 945 615 745 (799 in CO2) NEN NEO 02 418 607 498 C=C CEN C=0 839 891 1070 Table 9.2

Answer 1

soln-(a) civen - Bord energy of HI = 295 kJ/mol 1 (From Table) To find longest wavelength in nm) that can olissociate a molecule of HI. Formula used. h-plauk's constant c- speed of light t = 3x108 m/s 2 - wavelength h = 6.63810 34 Jos E- Energy Here {= 295 kJ/mol = 295 kJ/molecule NA NA= 6:023x1023 À = 6:63 71634 x 3x160 - XNA 295 x 1000 na 6.63 710034x 3 x 109 x 6.023X1023 295 X1000 = 406mm Longest wavelength lin nm) that. dissociate a molecule of HI is yobum. Hence, can

(b) of a photon of 226um is used, what is the excess energy (in I) over that needed for the dissociation. E = hCNA E = 6,63 410-3143 +10% 6.023X1023 226 470-9 3) E= 530 kJ 3) E=5.387055 Srcox, Daлoя и 2 сезо kJ - 29 к v = 235 kJ

Excess energy = 2.358107 I Mence, the excess energy over that needed for the dissociation is 2.35X105]. (0) y excess energy carried away by atom as kinetic energy, what is its speed (in m/s) Formula used- KE = Ź mu? KE = 2-35 yorg Mere -27 m= 1.67X102 kg 2:35x10r = 3 X1.67 810-27X V2 ve 1.68 710/6 m/s Hence, the speed of M-atam is 1.68x10 m/s