lect_15nov19f09-1

# lect_15nov19f09-1 - Outline 15 19-NOV-2009 1...

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1 Outline 15 19-NOV-2009 1. Review- Combining Thermochemical Eqns, light waves, wavelength, frequency, c = λ ν, 2. Light Particles? Photons Planck, Einstein, E photon = h ν , example 3. Bohr Model of H Atom ? energy levels, example 4. Matter Waves de Broglie, λ = h/mυ

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2 Review: Combining Eqns & ΔH’s; Ex. 6.102, p. 255. Find ΔH for (1) PCl 3 (l) + Cl 2 (g) PCl 5 (s) from (2) P 4 (s) + 6 Cl 2 (g) 4PCl 3 (l); -1280 kJ/mol (1) (3) P 4 (s) + 10Cl 2 (g) 4PCl 5 (s) ; -1774 kJ/mol (2) (2) and (3) are formation reactions! Soln: Want 1 PCl 3 on left PCl 3 (l) →( 1/4) P 4 (s) + (6/4) Cl 2 (g); (1280/4)kJ Want 1 PCl 5 on right so divide (3) by 4. (1/4)P 4 (s) + (10/4) Cl 2 (g) PCl 5 (s) ; (-1774/4) kJ
3 Review: Combining Eqns & ΔH’s; Ex. (cont.) 6.102, p. 255 (cont.) . Find ΔH for (1) PCl 3 (l) + Cl 2 (g) PCl 5 (s) from (2) P 4 (s) + 6 Cl 2 (g) 4PCl 3 (l); -1280 kJ/mol (1) (3) P 4 (s) + 10Cl 2 (g) 4PCl 5 (s) ; -1774 kJ/mol (2) Soln: Combine eqns. PCl 3 (l) →( 1/4) P 4 (s) + (6/4) Cl 2 (g); (1280/4)kJ (1/4)P 4 (s) + (10/4) Cl 2 (g) PCl 5 (s) ; (-1774/4) kJ PCl 3 (l)+ (1/4)P 4 (s) + (10/4)Cl 2 (g) ( 1/4)P 4 (s) + (6/4) Cl 2 (g) + PCl 5 (s) Canceling gives eqn. (1) ΔH rxn1 = [(1280/4) + (-1774/4)] kJ/mol rxn 1 = -124 kJ/mol rxn1

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4 Speed of light ( in vacuo ) 3.00*10 8 m/s. If know one ( λ or ν) can calculate other. Wave Nature of Light: Review Waves are described by: frequency ( time periodicity ), ν (cycles/s) and wavelength ( space periodicity ), λ (m/cycle) Their mathematical product gives speed of wave, c [(m/cycle)*(cycles/s) = m/s] c = λν
5 Visible light extends from violet end near 400 nm to the red end near 800 nm. Beyond these extremes, electromagnetic radiation is not visible to human eye. Electromagnetic Spectrum The range of frequencies or wavelengths of electromagnetic radiation is called the electromagnetic spectrum . Next Slide.

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6 Electromagnetic Spectrum.
7 Particle Nature of Light; Photons By early 1900’s wave nature of light and particle nature of matter well established; but, that was about to change! Physics was confounded by: (1) Blackbody radiation (perfect absorber-emitter) Explain Intensity versus frequency of hot objects. (2) Photoelectric effect Explain why light causes current to flow. (3) Atomic spectra Explain why elements emit (absorb) only certain wavelengths.

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Particle Nature of Light; Photons Blackbody radiation: Max Planck (1900) explained the variation of intensity with frequency for blackbodies (perfect absorbers and emitters) by saying objects could emit only certain energy quantities: E n = n h ν = 0,1,2,3,… (quantum number); h = 6.626*10 -34 J*s (called Planck’s constant) and ν is the frequency. Energy Quantized! Comes in integer units!
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lect_15nov19f09-1 - Outline 15 19-NOV-2009 1...

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