Thermodynamics

1
Thermodynamics

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• Mr. Chan
• Northwestern University

2
Day 122

• 0-15 Discuss TEST, Submit syllabus
• 15-35 Energy, Heat, Heat Capacity
• 30-35 Water Balloon demo
• 35-43 Activity

3
Energy and Heat what is energy?

• Energy Capacity for doing work or supplying
  heat
• Work from Physics
• Example Lifting books
• Types of Energy
• Kinetic Energy
• Potential Energy
• Chemical
• Energy stored in chemicals because of their
  composition
• Gravitational (Physics)

4
Energy and Heat what is heat?

• Heat (q)
• Transfer of energy due to a temperature
  difference
• Flows from warmer object to cooler object
• Thermochemistry
• Study of heat changes that occur during chemical
  reactions and changes in state
• Heat capacity
• Amount of heat it takes to change an objects
  temperature by exactly 1 degree celsius
• Water one of the highest, metals low heat
  capacities
• What are calories?
• Heat needed for 1 g water 1 degree Celsius
• 1 Calorie 1000 calories
• 1 Joule (SI unit) 0.239 calories, 1 kcal 4186
  Joules
• Remember Gummi bear/Cheetos?

5
Day 123

• 0-5 Discuss HW
• 5-10 Warmup
• 10-25 Specific Heat
• Demo balloon/water
• 25-35 Prelab
• 35-43 Lab
• 0-43 Lab/Calculations

6
Specific Heat

• Beach scenario-
• Sand vs. Water
• Different materials have different capacities to
  absorb or release energy
• Different factors affect an objects heat
  capacity
• Specific Heat (Specific Heat Capacity)
• Amount of heat it takes to raise the temperature
  of 1 gram of the substance 1 degree Celsius
• List of Specific Heats
• Equation C q/m (delta) T
• Practice
• Temperature of copper with mass 95.4 g changes
  from 25 C to 48 C when metal absorbs 849 Joules
  of heat. What is the specific heat of copper?

7
PreLab Calculating Specific Heat Capacity

• Dependent on 3 factors (working backwards from
  QmC?T)
• Energy transferred
• Mass
• Change in temperature
• Calculating in experiment (lab today)
• Practice 1-3

8
Lab Specific Heat of a Metal (A/W 15)

• Objectives
• Measure specific heat of lead
• Identify an unknown metal from its specific heat
• Techniques
• Calorimetry
• Calculations with Specific Heat
• Identifying an Unknown
• Hypothesis
• Rank in order of increasing specific heat
  water, zinc, aluminum, lead
• Why is a foam coffee cup used instead of a beaker?

9
Day 124

• 0-10 discuss HW w/selected answers
• 10-15 Warmup
• 15-30 Exothermic and endothermic processes,
  Calorimetry
• 30-43 PostLab, HW Head Start

10
Calculating Heat Changes

• Calorimetry
• Measurement of heat change for chemical and
  physical processes
• Measuring in Labs
• Calorimeter
• Insulated device that measures absorption or
  release of heat in chemical or physical
  processes.
• What does transfer of heat depend on?
• Q mC?T
• Mmass of water
• Cspecific heat
• ?Tchange in temperature
• System vs. Surroundings
• Total energy in universe conserved Law of
  conservation of energy
• Energy transfer between system and surroundings

11
Enthalpy

• Heat content of a system at constant pressure
• Heat change ?H
• Q ?H mC?T
• Negative exo, positive endo
• Practice 11-12
• Postlab calculating heat changes water C
  4.184 J/g K or 4,184 J/kg K
• Discuss calculations

12
Exothermic and Endothermic Processes

• Endothermic absorbs heat (delta H is positive
  heat flows in)
• Exothermic releases heat (delta H is negative
  heat flows out)

13
Calorimeter
14
Day 125

• 0-10 Discuss HW
• 10-15 warmup
• 15-25 PreLab
• 25-43, 0-43 Lab

15
Day 126 (Lab)

• 0-10 Warmup
• 10-30 Thermochemical Equations
• 30-43 HW Head Start

16
Heats of Reaction

• Heat change for equation exactly as written
• 2NaHCO3 129 kJ yields Na2CO3 H2O CO2
• 2NaHCO3 yields Na2CO3 H2O CO2 delta H 129
  kJ
• Show reaction, Delta H (negative vs. positive),
  per mole (look at coefficients)
• Standard conditions (1 atm pressure, 25 degrees
  Celsius)
• Practice 13-14
• Calculate the kJ of heat required to decompose
  2.24 mol of NaHCO3
• Consider physical state of reactants/products
• Calculate heats associated with reactions and
  amount of substances
• Heat of combustion
• Heat of reaction for burning of 1 mole of
  substance
• Practice
• C 2S yields CS2 delta H 89.3kJ
• Calculate amount of heat absorbed when 5.66 g of
  CS2 forms

17
Day 127

• 0-5 Discuss Lab, HW
• 5-25 QUIZ
• 25-40 Latent Heats, Heats of Solution
• 40-43 HW Head Start

18
Latent Heats

• What about energy gained or released when
  temperature does not change?
• Recall Heat of fusion lab what did this mean?
• Heat of fusion/solidification
• Energy gained or released when one mole melting
  or when liquid turns to solid
• Delta Hfusion - Delta Hsolid
• Water fusion (6.01 kJ/mol), solidification
  (-6.01kJ/mol)
• Heat of vaporization/condensation
• Energy gained or released when boiling or when
  gas turns to liquid
• Water condensation -40.7 kJ/mol, vaporization
  40.7 kJ/mol
• Practice 20-23
• How many grams of ice at 0 Celsius could be
  melted by the addition of 2.25 kJ of heat?
• How much heat is absorbed when 24.8 g of H2O is
  converted to steam?

19
Day 128

• 0-10 Discuss HW
• 10-15 Warmup
• Calculate enthalpy change for 2NO(g) O2(g)
  yields 2NO2(g)
• 15-25 Heats of Formation
• 25-43 Prelab
• Discuss QUIZ
• 0-43 Lab (with Cover Sheet)

20
Heat of Solution

• Heat change that occurs when one mole of solute
  dissolves in a solvent
• Exo NaOH in water, handwarmers NaOH yields Na
  OH- delta H -445.1 kJ/mol
• Endo NH4NO3, cold packs
• Practice 24-25
• How much heat is released when 2.50 mol of NaOH
  is dissolved in water?

21
Determining Heats of Reaction from Standard Heats
of Reactions

• Standard Heat Formation DeltaHf
• Change in enthalpy that accompanies the formation
  of one mole of compound from elements in their
  standard states
• Free elements in standard state is zero
• Others in appendix A.6 (note state of matter)
• Instead of manipulating equations, use standard
  heats to calculate ?H
• ?H products reactants
• List of Standard Heats (Table 11.6)
• Practice 30-31
• CH4(g) 2O2(g) yields CO2(g) 2H2O(l)
• 2SO2(g) O2(g) yields 2SO3(g)

22
HONORS How do we determine heats of reaction
for equations?

• Many heats of reaction cannot be measured in
  laboratory because they take too slow.
• Use mathematical method
• Hesss Law of heat summation
• Calculating Heats of Reaction by combining
  reactions
• Reverse reaction reverse sign
• Multiply reaction coefficients multiply ?H
• Add Reactions, Add ?Hs
• Practice
• 2H2O2(l) yields 2H2O(l) O2(g)
• H2(g) O2(g) yields H2O2(l) Delta H -187.9 kJ
• H2(g) 1/2O2(g) yields H2O(l) Delta H -285.8 kJ

23
Day 129, 130, 131

• Review, Test, Mythbusters, End of Quarter

24
Exit Slips

• Midterm Self Assessment
• Give yourself 2 grades
• 1) Class grade (estimate using HW, LABS,
  QUIZZES, and TESTS)
• 2) Effort grade
• Write a few sentences justifying your grades.