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!Hcomb of benzoic acid (C6H5CO2H) is -3227 kJ/mol. When a 2.442-g sample of benzoic acid is burned in a calorimeter, all of the resulting heat is transfered to 2.5 kg of water (c=4.184 J/g.K). What is the temperature change? Calculate !Hrxn for 2 NOCl N2 + O2 + Cl2 given the following set of reactions N2 + O2 2NO + Cl2 2NO 2NOCl !H = 180.6 kJ !H = -77.2 kJ Combustion of octane C8H18 produces carbon dioxide and water. C8H18 + O2 CO2 + H2O (a) Balance this reaction and calculate !Hocomb for 1 mol of octane, assuming water forms as a gas; !Hof = -208.45 kJ/mol for octane !Hof = -393.5 kJ/mol for carbon dioxide !Hof = -241.8 kJ/mol for H2O (g) (b) How many liters of CO2 (at 25 oC and 1 atm, R = 0.0821 atm.L/mol.K) are formed when 1 kg of octane is burned? How much work is done by the expanding CO2 as 1 kg of octane is burned (again, at 25 oC and 1 atm). (Hint, 1 J = 9.87.10-3 atm.L). What is !E for the reaction? (Hint, the definition of H = E + PV, assume PV is done by carbon dioxide only (ignore water and octane)) Atomic Structure: Quantum Theory nuclear model from Ratherford’s experiments Problem with Classic Structure accelerating charged particle loses energy The Nature of Light ! frequency (") ! amplitude #= c " Electromagnetic Spectrum Diffraction and Interference diffraction interference here, light behaves as a wave Blackbody Radiation However: 0K 1000 K 1500 K Max Planck, 1900 E = nh" n is a positive whole number, quantum number h is a constant " is the frequency of light emitted Photoelectric Effect • threshold frequency • no time lag Einstein, ~1905 Ephoton = h" > 2000 K Photoelectric Effect 7.96. Electric power is typically stated in units of watts (1W = 1J/s). About 95% of the power output of an incandescent bulb is converted to heat and 5% to light. If 10% of that light shines on your chemistry text, how many photons per second shine on the book from a 75-W bulb? (assume a wavelenght of 550 nm) The Nature of Light • electromagnetic radiation travels in waves • at the speed of light (in vacuum, c = "#) • intensity is either amplitude or number of photons/second • energy of light is quantized, E = h" • the energy of atom is also quantized, E = nh" h = 6.626$10-34 J•s Atomic Spectra H He Na sunlight Ba K Atomic Spectra (Neon) Atomic Spectra (H) Rydberg equation 1 =R ! 1 22 _ 1 n2 The Bohr Model of the Hydrogen Atom Niels Bohr proposed these postulates: 1. The H atom has fixed energy levels: stationary states 2. The atom does not radiate energy while in one of those states 3. Change to another state: !E = !Ephoton = h" The Bohr Model of the Hydrogen Atom Niels Bohr proposed these postulates: E = h! ground state: the lowest energy The Bohr Model of the Hydrogen Atom E = h! the charge of the nucleus -18 E = -2.18x10 J Z2 n2 energy levels for the H atom De Broglie: electrons are waves matter is wavelike: #= h mv electrons within atoms behave like waves The Quantum-Mechanical Model Schrodinger equation: d2% d2% d2% 8&2me [E - V(x,y,z)]%(x,y,z)=0 + + + dx2 dy2 dz2 h2 or H% = E% %2 is the probability that the electron is in a certain region of space The Quantum-Mechanical Model Schrodinger equation: H% = E% solutions (energy states) are associated with a given %, called an atomic orbital Hydrogen Atom “point” probability radial probability Hydrogen Atom 32% 74% 99% Atomic Orbitals different energy states are associated with atomic orbitals atomic orbitals are characterized by 4 (3) quantum numbers n (1,2,3, etc.) is the size (level) principal quantum number l (from 0 to n-1) is the shape (sublevel) angular momentum quantum number ml (from -l to +l) is the orientation magnetic quantum numbber Atomic Orbitals Sample Problem 7.5 Specify possible orbitals (sets of n, l, m) for n=3. Atomic Orbitals n (level) 1,2,3, etc l (sublevel, shape) s (l=0), p (l=1), d (l=3), f(l=4), etc S orbital - m equals 0 Atomic Orbitals (s) 1 s orbital 3 s orbital