Wednesday, Oct. 21st:

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Happy Mole Day!

• Mole day is celebrated every October 23rd between
  602 in the morning and 602 in the evening.
• Scientists celebrate mole day because the mole is
  the SI base unit for the amount of a substance.
• The number of particles in 1 mole of any
  substance is 6.022 X 1023, which is Avogadros
  number.

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Just How Big is a Mole?

• Avogadro's number of pennies placed side by side
  would stretch for more than 1 million light
  years!
• This amount of pennies would also be good enough
  to repay the debt of United States of America 86
  million times!

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• Why is Avogadro so rich?
• He's a multi-mole-ionaire!
• What did Avogadro teach his students in math
  class?
• Moletiplication
• Why did Avogadro stop going to a chiropractor on
  October 24th?
• He was only tense to the 23rd.

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Wednesday, Oct. 23rd A Day Thursday, Oct.
24th B DayAgenda

• Ch. 9 Stoichiometry Tests
• Homework questions/collect
• Sec.10.1 quiz Energy Transfer
• Section 10.2 Using Enthalpy
• Molar enthalpy changes, enthalpy changes of
  exothermic/endothermic reactions, enthalpy of a
  system, thermodynamics
• Homework
• Sec 10.2 review, pg. 349 1-8
• Concept Review Using Enthalpy
• Quiz next time over section 10.2

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Ch 9 Stoichiometry Tests
Class Average Score (out of 60) Average Percentage
3A 52.68 87.80
4B 52.86 88.10
In general, I was really pleased with these
scoreswell done!
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Homework Questions/Problems

• Pg. 344 1-12, 14, 15

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Ch 10 Causes of Change

• What happened?
• Why?

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QuizSection 10.1 Energy Transfer

• You may use your notes and/or your book.
• (Question 10 M molar mass)
• Good Luck!

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Section 10.2 Using Enthalpy

• Molar enthalpy change the change in enthalpy
  for one mole of a pure substance.
• Symbol ?H
• Unit J/mol (or kJ/mol)
• When a pure substance is only heated or cooled,
  the amount of heat involved is the same as the
  change in enthalpy , ?H.

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Molar Enthalpy Change

• Fe (s, 300 K) Fe (s, 1,100 K)
• ?H 20.1 kJ/mol
• This equation indicates that when 1 mol of solid
  iron is heated from 300 K to 1,100 K its molar
  enthalpy increases by 20,100 joules (20.1 kJ).

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Molar Heat Capacity Governs the Changes

• The iron that the blacksmith uses does not change
  state and is not involved in a chemical reaction.
• When a pure substance is only heated or cooled,
  ?H q SO
• ?H C?T
• (Molar enthalpy change)
• (molar heat
  capacity)(temp change)
• This reaction does NOT apply to chemical
  reactions or changes of state.

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Calculating Molar Enthalpy Change for Heating,
Sample Problem B, pg. 346

• How much does the molar enthalpy change when ice
  warms from -5.4C to -0.2C?
• ?H C?T
• C 37.4 J/Kmol (heat capacity for solid water
  from Table 1 on pg. 343)
• ?T (-0.2) (-5.4) 5.2 K
• ?H (37.4 J/Kmol) (5.2 K)
• ?H 190 J/mol
• (2 sig figs)

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Calculating Molar Enthalpy Change for Heating,
Practice 1, pg. 346

• Calculate the molar enthalpy change of H2O(l)
  when liquid water is heated from 41.7C to
  76.2C.
• ?H C?T
• C 75.3 J/Kmol (heat capacity for liquid water
  from Table 1 on pg. 343)
• ?T 76.2 41.7 34.5 K
• ?H (75.3 J/Kmol) (34.5 K)
• ?H 2.60 X 103 J/mol
• (3 sig figs)

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Calculating the Molar Enthalpy Change for
Cooling, Sample Problem C, pg. 347

• Calculate the molar enthalpy change when an
  aluminum can that has a temperature of 19.2C is
  cooled to a temperature of 4.00C.
• ?H C?T
• C 24.2 J/Kmol (heat capacity for Al from
  Table 1 on pg. 343)
• ?T 4.00 19.2 -15.2 K
• ?H (24.2 J/Kmol) (-15.2 K)
• ?H -368 J/mol
• (3 sig figs)

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Calculating the Molar Enthalpy Change for
Cooling, Practice 1, pg. 347

• The molar heat capacity of Al(s) is
• 24.2 J/Kmol. Calculate the molar enthalpy
  change when Al (s) is cooled from 128.5C to
  22.6C.
• ?H C?T
• C 24.2 J/Kmol
• ?T 22.6 128.5 -105.9 K
• ?H (24.2 J/Kmol) (-105.9 K)
• ?H -2,560 J/mol
• (3 sig figs)

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Enthalpy Changes of Endothermic or Exothermic
Processes

• In example problem B, ice was warmed and the
  enthalpy change was positive, meaning that energy
  was added or absorbed.
• In example problem C, an aluminum can was cooled
  and the enthalpy change was negative, meaning
  that energy was released.
• Positive ?H endothermic reaction
• Negative ?H exothermic reaction

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Enthalpy of a System

• Thermodynamics the branch of science concerned
  with the energy changes that accompany chemical
  and physical changes.

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In-Class/Homework

• Section 10.2 Review, Pg 349 1-8
• Concept review Using Enthalpy
• Quiz next time over section 10.2