Friday, Oct. 25 th : “A” Day Monday, Oct. 28 th : “B” Day Agenda

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Friday, Oct. 25 th : A Day Monday, Oct. 28 th : B Day Agenda. Homework questions/Quick review Section 10.2 Quiz: Using Enthalpy Section 10.3: Changes in Enthalpy During Chemical Reactions - PowerPoint PPT Presentation

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<ul><li><p>Friday, Oct. 25th: A DayMonday, Oct. 28th: B DayAgendaHomework questions/Quick reviewSection 10.2 Quiz: Using EnthalpySection 10.3: Changes in Enthalpy During Chemical Reactions Calorimetry, calorimeter, adiabatic calorimetry, Hesss Law, standard enthalpy of formationHomeworkPg. 15 practice worksheet (MUST show work)Sec. 10.3 review, pg. 357: #1-5Concept Review: Changes in Enthalpy During Chemical Reactions</p></li><li><p>Homework Questions/ProblemsPg. 349: #1-8</p></li><li><p>Section 10.2 Quiz: Using EnthalpyYou can use both your book and your notes.Youll need both 10.1 AND 10.2 notes.</p><p>May the FORCE bewith you!#4: M = molar mass#8: Use the 25 J rule</p></li><li><p>Changes in Enthalpy Accompany ReactionsChanges in enthalpy occur during chemical reactions.A change in enthalpy during a reaction depends on many variables, but temperature is one of the most important variables.</p><p>To standardize enthalpies of reaction, data are presented for reactions in which both reactants and products have the standard thermodynamic temperature of 25C or 298.15 K.</p></li><li><p>Chemical CalorimetryCalorimetry: the measurement of heat-related constants, such as specific heat or latent heat.</p><p>Calorimeter: a device used to measure the heat absorbed or released in a chemical or physical change.</p></li><li><p>Nutritionists Use Bomb Calorimetry A bomb calorimeter is used to measure enthalpy changes caused by combustion reactions.</p></li><li><p>Adiabatic Calorimetry is Another StrategyInstead of using a water bath to absorb the energy generated in a combustion reaction, adiabatic calorimetry uses an insulating vessel that doesnt allow energy to pass through.As a result, the temperature of the reaction mixture will change and can be recorded.Adiabatic calorimetry is used for reactions that are not ignited, such as for reactions in aqueous solution.</p></li><li><p>Hesss LawHesss Law: the law that states that the amount of heat released or absorbed in a chemical reaction does not depend on the number of steps in the reaction.</p><p>The overall enthalpy change in a reaction is equal to the sum of the enthalpy changes for the individual steps in the process.</p></li><li><p>Standard Enthalpies of FormationStandard enthalpy of formation: the enthalpy change in forming 1 mol of a substance from elements in their standard state.</p><p> By definition, the values of the standard enthalpies of formation for elements are zero.</p><p>Symbol: HfUnit: kJ/mol</p></li><li><p>Calculating Enthalpy Change for a Chemical ReactionUsing a list of standard enthalpies of formation, the enthalpy change of any reaction for which there is data available can be calculated:Hreaction = Hfproducts - Hfreactants</p><p>Hreaction is in kJ or Joules (moles cancel out)</p></li><li><p>Table 2: Standard Enthalpies of Formation</p></li><li><p>ExampleCalculate the enthalpy change for the following reaction. Use the standard enthalpies of formation listed in Table A-11 on pg 833-834.HCl(g) + NH3(g) NH4Cl(s)Hreaction = Hf0products - Hf0reactants</p><p>Hf0product = (1 mol)(-314.4 kJ/mol) = -314/4 kJ Hf0reactants=[(1 mol)(-92.3 kJ/mol)+(1 mol)(-45.9 kJ/mol)] = -138.2 kJHreaction = (-314.4 kJ) (-138.2 kJ) -176.2 kJ (exothermic reaction)</p></li><li><p>Additional PracticeCalculate the enthalpy change for the following reaction. Use the standard enthalpies of formation listed in Table A-11 on pg 833-834.N2(g) + 3 H2(g) 2 NH3(g) State whether the reaction is exothermic or endothermic.Hreaction = H f0products - H f0reactantsHf0prod = [(2 mol)(-45.9 kJ/mol) = -91.8 kJHf0reactants = [(1 mol)(0 kJ/mol) + (3 mol)(0 kJ/mol)] = 0 kJHreaction = (-91.8 kJ) (0 kJ) = -91.8 kJ*Reaction is exothermic because H is negative.*</p></li><li><p>Calculating a Reactions Change in Enthalpy Sample Prob. E, pg.356Calculate the change in enthalpy for the reaction below using data from Table 2 on pg 355.2 H2(g) + 2 CO2(g) 2 H2O(g) + 2 CO(g)State whether the reaction is exothermic or endothermic.Hreaction = H f0products - H f0reactantsHf0prod = [(2 mol)(-241.8 kJ/mol) + (2 mol)(-110.5 kJ/mol)]= -704.6 kJHf0reactants = [(2 mol)(0 kJ/mol) + (2 mol)(-393.5 kJ/mol)]= -787 kJHreaction= (-704.6 kJ) (-787 kJ) = 82.4 kJ*Reaction is endothermic because H is positive.*</p></li><li><p>HomeworkPg. 15 practice workshetMUST show work!Section 10.3 review, pg. 357: #1-5Concept Review: Changes in Enthalpy During Chemical Reactions</p></li></ul>