e1f08 - Version PREVIEW Exam 1 JOHNSON (53755) 1 This...

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Unformatted text preview: Version PREVIEW Exam 1 JOHNSON (53755) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. LDE Planck relation 001 001 10.0 points What is the energy, in Joules, of a photon of wavelength 200 nm? What bond energy would this correspond to, in kJ mole- 1 ? 1. 1 . 32 10- 40 J; 7.95 10- 20 kJ mole- 1 2. 9 . 94 10- 17 J; 1.65 10- 43 kJ mole- 1 3. 9 . 94 10- 19 J; 599 kJ mole- 1 correct 4. 1 . 32 10- 21 J; 795 kJ mole- 1 5. 9 . 94 10- 21 J; 5.99 kJ mole- 1 6. 1 . 32 10- 31 J; 7.95 10- 11 kJ mole- 1 Explanation: = 200 nm c = 3 10 8 m/s h = 6 . 626 10- 34 J s. For a photon c = , so E = h = h c where c is the speed of light and h is Plancks constant. E = h c = ( 6 . 63 10- 34 J s ) ( 3 10 8 m / s ) 1 200 nm 10 9 nm 1 m = 9 . 94 10- 19 J 9.94 10- 19 J 6 . 022 10 23 mol- 1 = 599 kJ mole- 1 LDE Classical Failure 001 002 10.0 points Which of the following statement(s) is/are true? I) Classical mechanics accurately predicted the behavior of blackbody radiators. II) The failure of classical mechanics to pre- dict the behavior of blackbody radiators is called the ultraviolet catastrophe. III) A minimum frequency of light is required to eject an electron from a metal surface. IV) The emission spectra of gases are con- tinuous rather than discrete. 1. I, II and IV 2. II, III, and IV 3. II and III correct 4. III and IV 5. I and III Explanation: Classical mechanics predicted that the power radiated by a blackbody radiator would be proportional to the square of the fre- quency at which it emitted radiation, and thus approach infinity as the frequency in- creased. This was false, since at higher fre- quencies blackbody radiators emit less, not more power. This was termed the ultraviolet catastrophe. Classical mechanics also pre- dicted that the energy (velocity) of electrons emitted from a metal surface is proportional to the intensity of light. In reality, the en- ergy (velocity) is only dependent upon the frequency of light. Once the threshold fre- quency is reached, however, the number of emitted electrons is proportional to the in- tensity of light. Classical mechanics also fails in explaining the discrete lines in ab- sorption/emission spectrum, which are due to discrete energy levels of atoms. LDE Rydberg Calc 001 003 10.0 points For the Hydrogen atom, an electron mov- ing between which two energy levels in the Balmer series would have to absorb light with a frequency ( ) of 6.19 10 14 Hz? 1. n = 2 and n = 3 2. n = 1 and n = 3 Version PREVIEW Exam 1 JOHNSON (53755) 2 3. n = 3 and n = 5 4. n = 2 and n = 4 correct 5. n = 1 and n = 4 6. n = 1 and n = 2 Explanation: A frequency of 6.19 10 14 Hz corresponds to a transition from n = 2 to n = 4 using the Rydberg equation. The fact that the Balmer series is mentioned also indicates that n...
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This note was uploaded on 03/04/2011 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.

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e1f08 - Version PREVIEW Exam 1 JOHNSON (53755) 1 This...

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