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CHEM120 Midterm #2 Review November 10, 2010

CHEM120 Midterm #2 Review November 10, 2010. Outreach Trip. 2. Introduction. Marie Leung, SOS CHEM120 Coordinator/Tutor A little about me... Also a CHEM120L TA =) 4A Biomedical Sciences Glee Addict!. 3. 2. Outline of Session. Chapter 7: Thermochemistry introduction to energy systems

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CHEM120 Midterm #2 Review November 10, 2010

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  1. CHEM120 Midterm #2 Review November 10, 2010

  2. Outreach Trip 2

  3. Introduction • Marie Leung, SOS CHEM120 Coordinator/Tutor • A little about me... • Also a CHEM120L TA =) • 4A Biomedical Sciences • Glee Addict! 3 2

  4. Outline of Session • Chapter 7: Thermochemistry • introduction to energy systems • heats of reaction • pressure-volume work • first law of thermodynamics • enthalpy, ∆H & Hess’s Law 4 4

  5. Outline of Session • Chapter 8: Electrons in Atoms • electromagnetic radiation • introduction to quantum theory • quantum numbers and electron orbitals • electron configurations • Question and Answer Period 5 5

  6. Chapter 7: Thermochemistry 6

  7. Chapter 7: Thermochemistry • Introduction to Energy Systems • system vs surroundings • types of systems: • open system • closed system • isolated system • types of energy: • kinetic • thermal • potential 7

  8. Chapter 7: Thermochemistry • Heat • energy that is transferred between a system and its surroundings, as a result of a temperature difference • quantity of heat, q (in joules): • m= mass of substance (in grams) • c = specific heat capacity (in J/g•°C) • ∆t = change in temperature (°C) q = mc∆t 8

  9. Chapter 7: Thermochemistry • Heat • energy that is transferred between a system and its surroundings, as a result of a temperature difference • quantity of heat, q (in joules) • exothermic reaction: qrxn < 0 • endothermic reaction: qrxn > 0 q = mc∆t 9

  10. Chapter 7: Thermochemistry • Enthalpy, ∆H • measure of total energy of system • measured in kJ or kJ/mol (depending on situation) • q = quantity of heat (in joules) • n = moles ∆H = q/n 10

  11. Chapter 7: Thermochemistry • Heat ex. 1: Given 8.27 g of H2O (specific heat = 4.18 J/g•°C), how much heat is required to raise the temperature from 25°C to 99°C? 11

  12. Chapter 7: Thermochemistry • Heat & Law of Conservation of Energy • energy cannot be added to or taken away from the universe, but is simply transferred between a system and its surroundings qsystem + qsurroundings = 0 12

  13. Chapter 7: Thermochemistry • Heat & Law of Conservation of Energy ex. 2: A 1.22-kg piece of iron at 126.5°C is dropped into 981 g of water at 22.1°C. The temperature rises to 34.4°C. Determine the specific heat of iron, in J/g•°C. 13

  14. Chapter 7: Thermochemistry • Heat & Calorimetry ex. 3: The combustion of 1.010g sucrose (MC12H22O11 = 342.3g), in a bomb calorimeter causes the temperature to rise from 24.92°C to 28.33°C. The heat capacity of the calorimeter assembly is 4.90 kJ/°C. a. what is the heat of combustion of sucrose? b. how much energy is present in one teaspoon (i.e. 4.8g) of sucrose? 14

  15. Chapter 7: Thermochemistry • Pressure-Volume Work • work involved in the expansion or compression of gases Let’s think about a few scenarios... • constant volume (an isochoric process) w = -Pext x (0) = 0 = NO WORK! • constant pressure • isobaric expansion (∆V is positive) -Pext x (+V) = negative work • isobaric compression (∆V is negative) -Pext x (-V) = positive work w = -Pext x ∆V 15

  16. Chapter 7: Thermochemistry • Pressure-Volume Work ex. 4: How much work, in joules, is involved when 0.225 mol N2 (at a constant temperature of 23°C) is allowed to expand 1.50 L against a Pext of 0.750atm? 16

  17. Chapter 7: Thermochemistry • First Law of Thermodynamics • states the relationship between heat (q), work (w) and changes in internal energy (∆U) • in an isolated system, ∆U = 0, and thus, the energy of an isolated system is constant • sign conventions: • +q, +w: energy entering system (i.e. heat absorbed by system, or work done on system) • -q, -w: energy leaving system (i.e. heat released by system, or work done by system) ∆U = q+ w 17

  18. Chapter 7: Thermochemistry • First Law of Thermodynamics • ex. 5: In compressing a gas, 355 J of work is done on the system, while 185 J of heat is released from the system. Find ∆U. • sign conventions: 18

  19. Chapter 7: Thermochemistry • Enthalpy, ∆H • we know that: • under constant temperature and pressure: • therefore: ∆U = q+ w w = -P∆V qP = ∆H ∆U = ∆H- P∆V 19

  20. Chapter 7: Thermochemistry • Enthalpy, ∆H • ex. 6: For which of the following combustion reactions is ΔU = ΔH? A. CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) B. C2H5OH(l) + 3 O2(g) → 2 CO2(g) + 3 H2O(l) C. C4H9OH(l) + 6 O2(g) → 4 CO2(g) + 5 H2O(l) D. none of the above 20

  21. Chapter 7: Thermochemistry • Hess’s Law & Heats of Formation • Guidelines: • 1. When reaction is multiplied or divided, multiply or divide ∆H by the same value. • 2. The sign for ∆H changes when reaction is reversed. • 3. When the reactions are summed together, the ∆H can be determined by summing together the ∆H of each individual reaction. 21

  22. Chapter 7: Thermochemistry • Hess’s Law & Heats of Formation • ex. 7: Find C2H4 (g) + H2 (g) C2H6 (g) C2H4 (g) + 3 O2 (g) 2 CO2 (g) + 2 H2O (l) ∆H = -1411 kJ C2H6 (g) + 7/2 O2 (g) 2 CO2 (g) + 3 H2O (l) ∆H = -1560 kJ H2 (g) + ½ O2 (g) H2O (l) ∆H = -285.8 kJ 22

  23. Chapter 8: Electrons in Atoms 23

  24. Chapter 8: Electrons in Atoms • Intro to Electromagnetic Radiation: • c = speed of light ≈ 3 x 108 m/s • ν = frequency (in s-1, or Hz) • λ = wavelength (in m) c = λν higher frequency shorter wavelength lower frequency longer wavelength 24

  25. Chapter 8: Electrons in Atoms Lawrence Berkeley National Laboratory http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html 25

  26. Chapter 8: Electrons in Atoms • Quantum Theory • Planck’s Equation • E = energy (in J) • h = Planck’s constant, 6.62607 x 10-34 J•s • note the trends: • shorter wavelength = higher frequency = higher energy • longer wavelength = lower frequency = lower energy E = hν = hc/λ 26

  27. HIGHEST ENERGY LOWEST ENERGY LOWEST FREQUENCY HIGHEST FREQUENCY LONGEST WAVELENGTH SHORTEST WAVELENGTH Chapter 8: Electrons in Atoms ...going back to the electromagnetic spectrum:

  28. Chapter 8: Electrons in Atoms • Electromagnetic Spectrum • Ex. 8: Which of the following has the highest energy? • A. red light • B. microwaves • C. ultraviolet radiation • D. radiowaves

  29. Chapter 8: Electrons in Atoms • Brief Overview of Quantum Mechanics • Heisenberg Uncertainty Principle: • we cannot know the exact position and momentum of an electron at the same time • that is, if we know one variable, we do not know the other

  30. Chapter 8: Electrons in Atoms • Quantum Numbers and Electron Orbitals • 1. principal quantum number, n • shell number • must be positive, nonzero integral value • n = 1, 2, 3, 4... • i.e. “the neighbourhood” 30

  31. Chapter 8: Electrons in Atoms • Quantum Numbers and Electron Orbitals • 2. orbital angular momentum quantum number, ι • may be zero or a positive integer • must not be larger than n-1 • ι = 0, 1, 2, 3... (n-1) • corresponds to subshells: • s: ι =0 • p: ι =1 • d: ι =2 • f: ι =3 • i.e. “the street” 31

  32. Chapter 8: Electrons in Atoms • Quantum Numbers and Electron Orbitals • 3. magnetic quantum number, mι • may be negative, zero or a positive integer • ranges from -ι to +ι • refers to number of orbitals • e.g. if ι =1 (i.e. p subshell), mι = -1, 0, 1 • thus, there are three p orbitals (and 2 electrons in each one - total 6 e-) • i.e. “the house” 32

  33. Chapter 8: Electrons in Atoms • Quantum Numbers and Electron Orbitals • 4. electron spin number, ms • either+1/2 or -1/2 • two electrons per orbital - spin in opposite directions 33

  34. Chapter 8: Electrons in Atoms • Quantum Numbers and Electron Orbitals • ex. 9: Which of the following sets of quantum numbers are allowed? • a. n = 3, ι = 2, mι = -1 • b. n = 1, ι = 2, mι = 0 • c. n = 4, ι = 4, mι = 3 • d. n = 1, ι = 0, mι = 0 • e. n = 2, ι = 1, mι = -1 34

  35. Chapter 8: Electrons in Atoms • Quantum Numbers and Electron Orbitals • wavefunction, Ψ • how electron behaves in orbital • electron density, Ψ2 • probability of finding electrons at one point at • distance r from nucleus • radial probability distribution, 4πr2Ψ2 • probability of finding electrons at all points distance • r from nucleus

  36. Chapter 8: Electrons in Atoms • Quantum Numbers and Electron Orbitals • the ORBITRON.... http://winter.group.shef.ac.uk/orbitron/

  37. Chapter 8: Electrons in Atoms Orbital Diagram 2s Dr. Richard Bader, McMaster University http://www.chemistry.mcmaster.ca/esam/Chapter_3/section_2.html Wavefunction (atomic orbital) Radial Probability Distribution Dr. Richard Oakley, University of Waterloo http://www.science.uwaterloo.ca/~oakley/chem120/notes/chapter_08.htm http://www.pci.tu-bs.de/aggericke/PC3e_osv/Kap_IV/Energiezustand.htm Take home message: s-orbitals Ψ, Ψ2 nonzero at r = 0!

  38. Chapter 8: Electrons in Atoms Orbital Diagram 2p Dr. Richard Bader, McMaster University http://www.chemistry.mcmaster.ca/esam/Chapter_3/section_2.html Wavefunction (atomic orbital) Radial Probability Distribution Dr. Richard Oakley, University of Waterloo http://www.science.uwaterloo.ca/~oakley/chem120/notes/chapter_08.htm http://www.pci.tu-bs.de/aggericke/PC3e_osv/Kap_IV/Energiezustand.htm

  39. Chapter 8: Electrons in Atoms Orbital Diagram 3d Dr. Richard Bader, McMaster University http://www.chemistry.mcmaster.ca/esam/Chapter_3/section_2.html Wavefunction (atomic orbital) Radial Probability Distribution Dr. Richard Oakley, University of Waterloo http://www.science.uwaterloo.ca/~oakley/chem120/notes/chapter_08.htm http://www.pci.tu-bs.de/aggericke/PC3e_osv/Kap_IV/Energiezustand.htm

  40. Chapter 8: Electrons in Atoms Orbital Diagram 4f Dr. Richard Bader, McMaster University http://www.chemistry.mcmaster.ca/esam/Chapter_3/section_2.html Wavefunction (atomic orbital) Dr. Richard Oakley, University of Waterloo http://www.science.uwaterloo.ca/~oakley/chem120/notes/chapter_08.htm

  41. Chapter 8: Electrons in Atoms • Electron Configurations • 1. Electrons fill orbitals in a way that minimizes the energy of the atom • the aufbau principle • i.e. lowest energy levels are filled first

  42. Chapter 8: Electrons in Atoms • Electron Configurations • 2. No two electrons in an atom may have the same four quantum numbers • the Pauli exclusion principle • n, ι and mι determine the electron orbital • electrons that share the first three quantum numbers belong to the same shell, subshell and orbital

  43. Chapter 8: Electrons in Atoms • Electron Configurations • 3. Within orbitals of identical energy, electrons will first fill them singly before pairing up • Hund’s Rule • stability is associated with half filled or fully filled orbitals

  44. Chapter 8: Electrons in Atoms • Electron Configurations • ex 10. Determine the elements denoted by the following electron configurations: • a. • b. 1s22s22p63s1

  45. Chapter 8: Electrons in Atoms • Electron Configurations • ex 11. Draw electron configurations for each of the following elements: • a. potassium • b. copper

  46. Question & Answer Period 44

  47. Good Luck! • Further Questions? • Marie (mariejasmineleung@gmail.com) • For more information on Waterloo Students Offering Support, visit http://www.waterloosos.com/ 45

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