CHEM120 Midterm #2 Review
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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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Chem120 midterm 2 review november 10 2010

CHEM120 Midterm #2 Review

November 10, 2010


Outreach trip

Outreach Trip

2


Introduction

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

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


Chem120 midterm 2 review november 10 2010

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


Chapter 7 thermochemistry

Chapter 7: Thermochemistry

6


Chapter 7 thermochemistry1

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


Chapter 7 thermochemistry2

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


Chapter 7 thermochemistry3

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


Chapter 7 thermochemistry4

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


Chapter 7 thermochemistry5

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


Chapter 7 thermochemistry6

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


Chapter 7 thermochemistry7

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


Chapter 7 thermochemistry8

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


Chapter 7 thermochemistry9

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


Chapter 7 thermochemistry10

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


Chapter 7 thermochemistry11

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


Chapter 7 thermochemistry12

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


Chapter 7 thermochemistry13

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


Chapter 7 thermochemistry14

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


Chapter 7 thermochemistry15

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


Chapter 7 thermochemistry16

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


Chapter 8 electrons in atoms

Chapter 8: Electrons in Atoms

23


Chapter 8 electrons in atoms1

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


Chapter 8 electrons in atoms2

Chapter 8: Electrons in Atoms

Lawrence Berkeley National Laboratory

http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html

25


Chapter 8 electrons in atoms3

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


Chapter 8 electrons in atoms4

HIGHEST ENERGY

LOWEST ENERGY

LOWEST FREQUENCY

HIGHEST FREQUENCY

LONGEST WAVELENGTH

SHORTEST WAVELENGTH

Chapter 8: Electrons in Atoms

...going back to the electromagnetic spectrum:


Chapter 8 electrons in atoms5

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


Chapter 8 electrons in atoms6

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


Chapter 8 electrons in atoms7

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


Chapter 8 electrons in atoms8

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


    Chapter 8 electrons in atoms9

    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


    Chapter 8 electrons in atoms10

    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


    Chapter 8 electrons in atoms11

    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


    Chapter 8 electrons in atoms12

    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


  • Chapter 8 electrons in atoms13

    Chapter 8: Electrons in Atoms

    • Quantum Numbers and Electron Orbitals

    • the ORBITRON....

    http://winter.group.shef.ac.uk/orbitron/


    Chapter 8 electrons in atoms14

    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!


    Chapter 8 electrons in atoms15

    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


    Chapter 8 electrons in atoms16

    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


    Chapter 8 electrons in atoms17

    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


    Chapter 8 electrons in atoms18

    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


    Chapter 8 electrons in atoms19

    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


    Chapter 8 electrons in atoms20

    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


    Chapter 8 electrons in atoms21

    Chapter 8: Electrons in Atoms

    • Electron Configurations

    • ex 10. Determine the elements denoted by the following electron configurations:

    • a.

    • b. 1s22s22p63s1


    Chapter 8 electrons in atoms22

    Chapter 8: Electrons in Atoms

    • Electron Configurations

    • ex 11. Draw electron configurations for each of the following elements:

    • a. potassium

    • b. copper


    Question answer period

    Question & Answer Period

    44


    Good luck

    Good Luck!

    • Further Questions?

      • Marie ([email protected])

      • For more information on Waterloo Students Offering Support, visit http://www.waterloosos.com/

    45


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