Chapter 7 -lecture 1

Chapter 7 -lecture 1 - General Chemistry I Fall 2007 Joann...

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Unformatted text preview: General Chemistry I Fall 2007 Joann S. Monko Chemistry 9th ed. Raymond Chang He Transfe - No Changein S at r tate q transfe d = (S rre H)(m T) ass)( Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. He Transfe with a Changeof S at r tate Changes of state involve energy (at constant T) Ice + 333 J/g (heat of fusion) -----> Liquid water q = (he of fusion)(m at ass) q = (333 J/g)(500 g) q = 1.7 x 105 J Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. He Transfe and Change of S at r s tate Liquid ---> Vapor Heat of Vaporization 2256 J/g for water Requires energy (heat). This is the reason a) you cool down after swimming. b) you use water to put out a fire. + energy Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. He ating/C ooling C urvefor Wate r Evaporate water Heat water Melt ice Note: T is constant as ice melts & as water evaporates. He & C at hange of S s tate What quantity of heat is required to melt 500. g of ice and heat the water to steam at 100 oC? Heat of fusion of ice = 333 J/g Specific heat of water = 4.2 J/gK Heat of vaporization = 2260 J/g +333 J/g +2260 J/g Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. He & C at hange of S s tate Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. What quantity of heat is required to melt 500. g of ice and heat the water to steam at 100 oC? 1. To melt ice q = m Hfusion q = (500. g)(333 J/g) = 1.67 x 105 J 1. To raise water from 0 oC to 100 oC q = m SH T q = (500. g)(4.2 J/gK)(100 - 0)K = 2.1 x 105 J 3. To evaporate water at 100 oC q = m Hvaporization q = (500. g)(2260 J/g) = 1.13 x 106 J 4. Total heat energy = 1.51 x 10 J = 1510 kJ A scie ntific way to m ice te - 250 g of te at a te pe ake d a a m ratureof 18.2 oCand 5 icecube (1 icecube= 15 g). What quantity of ice s will m lt and how m icewill bele floating in theglass? e uch ft Assum : icete has a spe he of 4.2 J/g K. e a cific at U need: the heat change in cooling the tea q = m SH T the heat change in melting the ice q = m Hfusion Law of Conservation of Energy : q tea + q ice = 0 ( m SH T ) + ( mice)(Hf) = 0 [(250 g) (4.2 J/g K) (273.2 K 291.4 K)] + [ mice (333 J/g)] = 0 (-19110 J) + (333 J/g mice) = 0 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. ELEC TROMAGNETI CRADI ATI ON wavelength Visible light Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Amplitude wavelength Ultaviolet radiation Node zero amplitude, intervals of /2. Wavelength, distance between successive points on a wave. Amplitude maximum height of a wave from the midline. Peaks high points Troughs low points Waves have a frequency: "nu", , and units are "cycles per sec" S-1 or hertz, Hz All radiation: = c c = velocity of light = 3.00 x 108 m/sec Long wavelength --> small frequency Short wavelength --> high frequency Increasing Frequency Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Increasing Wavelength Red light has = 700 nm. Calculate the frequency. =c -9 m 1 x 10 -7 m 700 nm = 7.00 x 10 1 nm Freq = 3.00 x 10 m/s 7.00 x 10-7 m 8 = 4.29 x 10 14 sec -1 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. -the approx. ranges ( ) and "colors" ROY G BIV -trends in energy, frequency and wavelengths. The Electromagnetic Spectrum Chang Chemistry, 8th ed. Quantization of Ene rgy Max Planck (1858-1947) Solved the "ultraviolet catastrophe" h = Planck's constant = 6.6262 x 10-34 Js E = h -Vib. atoms in a heated obj. yield electromag. radiation. -The vibs. are QUANTIZED: only certain vibs. with specific are allowed. -Assume a distribution of vibs. -Most light comes from intermediate . Max Intesity = of the intermed. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Photoelectric Effect A. Einstein (1879-1955) This experiment demonstrates the particle nature of light. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Photoelectric Effect Photoelectric cells: e-'s are ejected only if the is high enough. Obs.: if the is above the min. intensity = current (cuz more e-'s are ejected). Light has both: wave and particle type properties. Massless "particles" = PHOTONS packets of energy. E=h =hc Electromag. radiation stream o f photons intensity = # of photons hit surface/unit time intensity = # of e-'s Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. For ye llow light, with a wave ngth of 535 nm le : What is thee rgy of onephoton? ne What is thee rgy of onem of photons? ne ole 1. Convert nm to m 535 nm x 1 x 10-9 m = 5.35 x 10-7 m 1 nm 2. E = h c / E = (6.626 x 10-34 J s / photon) (3.00 x 108 m/s) 5.35 x 10-7 m E = 3.72 x 10-19 J/photon 3. Avogadro's Number! 3.72 x 10-19 J x 6.022 x 1023 photons = photon 1 mole Kotz &Treichel = 2.24 x 105J/mol (or 224 kJ/mol) Chemistry & Chemical Reactivity 5th ed. TheEle ctric Pickle Excited atoms can emit light. Soln' in pickle is excited electrically Light characteristic of Na+ ions Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Atom LineEm ic ission S ctra Nie Bohr pe ls Greatest contribution: built a simple model of the atom - based on understanding Niels Bohr (1885-1962) SHARP LINE EMISSION SPECTRA of excited atoms. Excited atoms emit light of only certain wavelengths. The wavelengths of emitted light depend on the element. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Spectrum of White Light Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Spectrum of Excited Hydrogen Gas LineS ctra of Othe Ele e pe r m nts High E Short High Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Low E Long Low Atom S ctra and Bohr ic pe (early 20th century) atomic structure: an (e-) traveled about the nucleus in an orbit. + Electron orbit 1. Any orbit should be possible & so is any energy. 2. But a charged particle moving in an electric field should emit energy. End result should be destruction! Bohr said classical view is wrong. New theory - The Bohr Model e- can only exist in certain discrete orbits - stationary states The e- is restricted to QUANTIZED energy states. Energy of state = - Rhc/n2 Kotz &Treichel where n = quantum no. = 1, 2, 3, 4, .... Chemistry & Chemical Reactivity 5th ed. Atom S ctra and Bohr ic pe If e-'s are in quantized energy states, then E of states can have only certain values: Sharp Line Spectra Chang Chemistry, 8th ed. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Atom S ctra and Bohr ic pe The potential energy of an e- in the nth level En = -Rhc Rhc = RH n2 R = Rydberg Constant = 1.097 x 107 m-1 H = Plank's Constant = 6.626 x 10-34 J s C = speed of light = 3.0 x 108 m/s E = Efinal Einitial E = Ef Ei = RH (1/n2initial - 1/n2final) where RH = 2.18 x 10-18 J Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Ele ctron Transitions E = h E = h Chang Chemistry, 8th ed. Origin of LineS ctra pe Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Quantumor WaveMe chanics L. de Broglie (1892-1987) de Broglie (1924) proposed that all moving objects have wave properties. For light: E = mc2 = h = hc / Therefore, mc = h / and for particles (mass)(velocity) = h / Baseball (114 g) at 110 mph = 1.2 x 10-34 m e- with velocity = 1.9 x 108 cm/s = 0.388 nm Experimental proof of wave properties of electrons Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. E. Schrodinger 1887-1961 Schrodinger applied idea of e-'s behaving as a wave to the problem of e-'s in atoms. WAVE EQUATION Solution gives set of math expressions called WAVE FUNCTIONS, Each describes an allowed energy state of an eQuantization introduced naturally. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Wave Functions is a function of distance and two angles. Each corresponds to an ORBITAL -- the region of space within which an e- is found. does NOT describe the exact location of the e-. is proportional to the probability of finding an e- at a 2 given point. = fn(n, l, m , m ) n = 1, 2, 3, 4, .... l s n=2 n=1 n=3 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Chang Chemistry, 8th ed. ...
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This note was uploaded on 04/08/2008 for the course CHEM 100 taught by Professor Monko during the Winter '08 term at Kutztown.

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