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# Chem 111 week 8 lecture notes 111/40551

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This 7 page Class Notes was uploaded by amatzoll@gmail.com Notetaker on Saturday October 31, 2015. The Class Notes belongs to 111/40551 at University of St. Thomas taught by Uzcategui-White in Summer 2015. Since its upload, it has received 14 views.

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Date Created: 10/31/15

Chemistry Week 8 Lecture Notes Stoichiometry of Thermochemical Equations o A thermochemical equation is a balanced equation that includes a change in H reaction 0 The sign of change in H indicates whether the reaction is exothermic or endothermic o The magnitude of the change in H is proportional to the amount of substance 0 The value of H can be used in a calculation in the same way as a mole ratio 0 Change in H 9 endothermic absorbing heat 0 Change in H H 9 exothermic releasing heat 635 18 58 s H2 g 9 H25 g H 202 k a Endo or exothermic exothermic b What is the change in H for the reverse reaction 202 k c What is the change in H when 26 mol of 58 reacts 26 mol 58 x 202 kJ18 mol 58 42 x 10 quot2 k d What is the change in H when 250 g of 58 reacts 250 g 58 x 1 mol 2566 g x 2022 kJ18 mol 58 157 k Hess s Law 0 The enthalpy of an overall reaction is the sum of the enthalpy of the individual steps 0 H overall H 1 H2 H3 0 Steps 645 1 Target reaction 9 look at reactants and products 2 Manipulate individual equations 0 Change the sign of H when you reverse the reaction 0 Multiply amount of mols of equation and H value by the same factor 3 Add manipulated equations Calculate H for 2 NOCI g 9 N2 g 02 g CL2 g Given the following equations 12 N2 g 2 02 g 9 NO g H 903 kJ NO g 12 Cl2 g 9 NOCI g H 386 kJ 1 Reverse equations 3 NO g 9 12 N2 g 12 02 g H 9o3 kJ NOcl g 9 NO g 12 Cl2 g H 386 k Multiply 2 NO g 12 N2 g 12 02 g 9 2N0 g 9 N2 g 02 g 2 H 903 1806 k 2 NOCI g 9 NO g 12 Cl2 g 9 2NOC g 9 2N0 g Cl2 g 2 H 386 kJ 772 k Add equations 2 NO g 9 N2 g 02 g 2NOC g 9 2N0 g Cl2 g 2NOC g 9 N2 g 02 g Cl2 g H 1806 k 772 k 1034 k 647 Write the balanced overall equation for the following processes and calculate the H overall 1 P4 5 6C02 g 9 4 PC3 g H 1148 k 2 4PC3 g 4C2 g 9 4 PC5 g H 460 k 3 P4 5 10C2 g 9 4PC5 g H 1608 k Standard Enthalpy of Reaction o Gases 9 measured under pressure of 1 atm ideal gas 0 Solution 9 1M concentration 0 Substance 9 1 atm 25 C H rxn sum of H products sum of H reactants 653 Calculate the H reaction for Ch4 g C2 g 9 CC4 HCl g CH4 g 4C2 g 9 CC4 l 4HC g Look in appendix for values 1 mol CC4 x 1390 kJmol 4 mol HCl x 9231 kJmol 1molCH4 x 7481 kJmol 4 mol Cl2 x 0000 kjmol 4334 k 655 Copper I oxide can be oxidized to copper II oxide CuZO s 12 02 g 9 2 CuO 5 H 1460 k Given H of CuZO 1686 kJmol and H of 02 g 0 kJmol find the H of CuO 5 1 mol CuZO x 1686 kJmol 12 mol 02 x 0 kJmol 146 k 2 mol CuO x H reactants 1686 kJ 1573 H reactants Chapter 7 Quantum Theory and Atomic Substance o The nature of light Energy and Electrons and wavelength oscillating 1 2 3 Electromagnetic Radiation o The wave properties of the electromagnetic radiation are described by three properties Frequency v number of waves that pass a given point in some unit of time cycle per second Units squot1 or 15 hertz Amplitude Y distance a wave travels in one cycle distance between successive crests or troughs high low points Units meters nanometers SI units A 10quot10 m angstroms Amplitude the height of the wave crest or depth of a torugh related to intensity of radiation Equations speed C Y x V 9 Y c V C 300 x 10quot8 ms Y increases V decreases Regions of the Electromagnetic Spectrum o Visible light 0 Light of a single wavelength monochromatic ex green laser light 0 Light of many wavelengths polychromatic white 0 Purple laser 9 higher frequency 9 can burn a hole Diffraction and Refraction o Diffraction Waves bend around small obstacles and spread out a small openings in entering into a region that would be shadowed deviation from wave s initial straight line Shows light shadow o Refraction When a wave passes from one medium to another at any angle except 90 and 0 degrees its line of travel changes at the interface due to the change in velocity of the wave Refraction is always accomplished by a wavelength and speed change and depends on the two media 0 Color depends on the wavelength We see an emission of color a refracted wavelength ex diamonds Energy and Frequency o Electromagnetic radiation is emitted with wavelengths that depend on the temperature Color depends on temperature The higher the energy the shorter the wavelength A solid object emits visible light when it is heated to about 1000 k This is called black body effect Color Intensity 0 Change with temperature 0 Color 9 wavelength and frequency 0 Temperature 9 energy 0 Planck s equation E energy n integer x h x V frequency H 6626 x 10 quot34J x s Planck s constant Quantum Theory of Energy 0 Any object including atoms can emit or absorb only certain quantities of energy 0 Energy is quantizied it occurs in fixed quantities each quantity quantum o A quanta hv o The energy emitted or absorbed radiation difference in atoms energy states Change in E change in n x h x V o Photoelectric effect when monochromatic light of sufficient frequency shines on a metal plate 9 current flows When light flows in electrons flow out 0 Energy of Photon 0 Proposed by Einstein 0 bundles of energy called photons 0 each atom changes its energy when it absorbs or emits one photon one particle of light E photon h V 77 Radio broadcasting music at quot950 on radio dial Unit AM frequencies are given in kHz Find wavelength in meters nanometers and angstroms C Y x V y c v 9 y 300 x 10 quot8 ms950 kHz x 1000 HzI kHz x squot1 1 Hz 316 m

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