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lect_21nov17f08

# lect_21nov17f08 - Outline 21 17-NOV-2008 1 ReviewCombining...

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1 Outline 21 17-NOV-2008 1. Review- Combining Thermochemical Eqns., light waves 2. Nature of light- A. Waves (cont.) wavelength, frequency, c = λ ν, amplitude B. Particles, Photons E photon = h ν , example 3. Bohr Model of H Atom ? energy levels, example

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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 so reverse (2)& divide by 4. 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 Quantum Theory & Atomic Structure (Repeated Slide!) Ch. 7 involves describing electrons in atoms. What are electrons doing in the atom? Why don’t the protons (+ charge) in nucleus capture the electrons (- charge)? Answer comes from studying light emitted and absorbed by elements, spectra. (slide 6) Need to learn about nature of light.
5 Wave Nature of Light (Repeated Slide!) Wave - continuously repeating change or oscillation in matter or in physical field. Light has wave properties. Light involves oscillations in electric and magnetic fields that travel through space.

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