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Happy Mole Day!

Happy Mole Day!. Mole day is celebrated every October 23 rd between 6:02 in the morning and 6:02 in the evening. Scientists celebrate mole day because the mole is the SI base unit for the amount of a substance.

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Happy Mole Day!

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  1. Happy Mole Day! • Mole day is celebrated every October 23rd between 6:02 in the morning and 6:02 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 Avogadro’s number.

  2. 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!

  3. 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.

  4. 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*

  5. Ch 9 Stoichiometry Tests In general, I was really pleased with these scores…well done!

  6. Homework Questions/Problems • Pg. 344: 1-12, 14, 15

  7. Ch 10: Causes of Change • What happened? • Why?

  8. QuizSection 10.1: “Energy Transfer” • You may use your notes and/or your book. (Question #10: M = molar mass) Good Luck!

  9. Section 10.2: “Using Enthalpy” • Molar enthalpy change: the change in enthalpy for one mole of a pure substance. • Symbol: ΔH • 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 , ΔH.

  10. Molar Enthalpy Change Fe (s, 300 K) Fe (s, 1,100 K) ΔH = 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).

  11. 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, ΔH = q SO… ΔH = CΔT (Molar enthalpy change) = (molar heat capacity)(temp change) • This reaction does NOT apply to chemical reactions or changes of state.

  12. Calculating Molar Enthalpy Change for Heating, Sample Problem B, pg. 346 • How much does the molar enthalpy change when ice warms from -5.4˚C to -0.2˚C? ΔH = CΔT C = 37.4 J/K∙mol (heat capacity for solid water from Table 1 on pg. 343) ΔT = (-0.2) – (-5.4) = 5.2 K ΔH = (37.4 J/K∙mol) (5.2 K) ΔH = 190 J/mol (2 sig figs)

  13. Calculating Molar Enthalpy Change for Heating, Practice #1, pg. 346 • Calculate the molar enthalpy change of H2O(l) when liquid water is heated from 41.7˚C to 76.2˚C. ΔH = CΔT C =75.3 J/K∙mol (heat capacity for liquid water from Table 1 on pg. 343) ΔT = 76.2 – 41.7 = 34.5 K ΔH = (75.3 J/K∙mol) (34.5 K) ΔH = 2.60 X 103 J/mol (3 sig figs)

  14. 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 19.2˚C is cooled to a temperature of 4.00˚C. ΔH = CΔT C = 24.2 J/K∙mol (heat capacity for Al from Table 1 on pg. 343) ΔT = 4.00 – 19.2 = -15.2 K ΔH = (24.2 J/K∙mol) (-15.2 K) ΔH = -368 J/mol (3 sig figs)

  15. Calculating the Molar Enthalpy Change for Cooling, Practice #1, pg. 347 • The molar heat capacity of Al(s) is 24.2 J/K·mol. Calculate the molar enthalpy change when Al (s) is cooled from 128.5˚C to 22.6˚C. ΔH = CΔT • C = 24.2 J/K∙mol • ΔT = 22.6 – 128.5 = -105.9 K • ΔH = (24.2 J/K∙mol) (-105.9 K) ΔH = -2,560 J/mol (3 sig figs)

  16. 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 ΔH = endothermic reaction Negative ΔH = exothermic reaction

  17. Enthalpy of a System • Thermodynamics: the branch of science concerned with the energy changes that accompany chemical and physical changes.

  18. In-Class/Homework • Section 10.2 Review, Pg 349: #1-8 • Concept review: “Using Enthalpy” *Quiz next time over section 10.2*

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