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Lon-Capa

Lon-Capa. 4 th HW assignment due Friday, 10/10, 5 pm. It is open now. 3 rd Quiz due Sunday, 10/12 by 10 pm. It will open Friday, 10/10 at 5 pm. Clicker Question. The following chemical reaction is exothermic: A 2 + B 2  2AB. This means: more stable higher average bond energies

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Lon-Capa

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  1. Lon-Capa • 4th HW assignment due Friday, 10/10, 5 pm. It is open now. • 3rd Quiz due Sunday, 10/12 by 10 pm. It will open Friday, 10/10 at 5 pm.

  2. Clicker Question The following chemical reaction is exothermic: A2 + B2 2AB. This means: more stable higher average bond energies a) Reactants Reactants b) Reactants Products c) Products Products d) Products Reactants e) I do not know.

  3. Exothermic Process

  4. Endothermic Process

  5. Thermodynamics vs. Kinetics

  6. Some Big Ideas • Low energy  low in potential energy  more stable. • If a system absorbs energy, the natural tendency is to release it. • That is, achieving low potential energy is “natural”. • Ground state preferred over excited state. • Energy is converted from one form to another but is NOT created nor destroyed. • First law of thermodynamics. • Energy is a state function (heat and work are not).

  7. The Piston, Moving a Distance Against a Pressure P, Does Work On the Surroundings

  8. Determining Hrxn • Since H = qp, measure the heat given off or required at constant pressure. This is termed calorimetry. • Since energy is conserved, we can often determine Hrxn for one reaction given values of Hrxn for others. Uses the principle in Hess’s Law. • Use standard enthalpies of formations for reactants and products (we have tables of these).

  9. A Coffee-Cup Calorimeter Made of Two Styrofoam Cups

  10. Clicker Question You drop 50.0 g of 100.0C metal into 100.0 g of 22.0C water. The final temperature of the water is 29.5C. Identify the metal. c(water) = 4.18 J/g C a) aluminum (c=0.89J/gC) b) iron (c=0.45J/gC) c) copper (c=0.20J/gC) d) lead (c=0.14J/gC) e) I do not know how to do this.

  11. Constant-Pressure Calorimetry • Can determine enthalpy change for chemical reactions that occur in solution. See Example 9.3 on page 376 of your text. • Can calculate ΔE and ΔH when PV work occurs. See Example 9.4 on page 378 of your text.

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