PSU CHEM 110 - Chemical Reactions Equilibrium Part 4

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Chemical Reactions: Equilibrium Part 4Chemical Reactions: Equilibrium Part 4Le Châtlier’s Principle and ReactionsLe Châtlier’s Principle and the Real WorldPractice ProblemPractice ProblemLe Châtlier and Haber-BoschHow Fast is Equilibrium Reached?Catalysts, Equilibrium, and RatesDemo: Peroxide DecompositionThermite Revisited…PhosphorusDietary CalciumDietary CalciumWhat You Should Know Final Concepts You Should Know:Chemical Reactions:Equilibrium Part 4CH110 FA11 SAS 1Prepare for Final ExamLecture 43: December 7thLecture 44: December 9thRead: Ch. 15.6 – 15.7Suggested Problems: BLB 15: 51,53,70; Packet 15: 11-13FINAL EXAMMonday, Dec. 12th, 2:30 PMCH110 FA11 SAS 2By the end of Today’s Lecture you should know:Calculations involving KeqPredicting the direction of a reaction using Q Le Châtlier’s PrincipleCatalysisKEY QUESTIONS: THE BIG PICTUREChemical Reactions:Equilibrium Part 4Do real reactions always proceed to completion?What forces drive the reaction process?How do the properties of heterogeneous reactions differ from homogeneous?Remember: macroscopic properties come from microscopic originsWhat is Le Châtlier’s Principle?When a system is disturbed, why does it attempt to return to equilibrium?How fast do systems reach equilibrium?CH110 FA11 SAS 3Consider the Following Reactions:Are these examples of Redox Reactions?Cr2O72-is orange and CrO42-yellow2CrO42-(aq) + 2H+(aq) → Cr2O72-(aq) + H2O(l) Cr2O72-(aq) + 2OH-(aq) → 2CrO42-(aq) + H2O(l)What will happen to the solution if I add acid?What will happen to the solution if I add base?Le Châtlier’s Principle and ReactionsAre these Neutralization Reactions?Le Châtlier’s Principle and the Real WorldCH110 FA11 SAS 4Example: the Haber-Bosch ProcessN2(g) + 3 H2(g)2 NH3(g)Catalytic synthesis of ammonia from nitrogen and hydrogen gasescat.Why is this important??• Commodity chemical that is important to economy• 13.6 million metric tons consumed in the U.S. in 2006 (U.S. Geological Survey, most recent data available)• Starting material for many other chemicals, from fertilizers to pharmaceuticalsPractice ProblemCH110 FA11 SAS 5N2(g) + 3H2(g) 2NH3(g)In the Haber-Bosch process above, the following equilibrium concentrations of NH3, N2, and H2were determined at 472oC. What is Kp for these conditions?[H2] = 0.1207 M[N2] = 0.0402 M[NH3] = 0.00272 MA) 2.79x10-5B) 1.71x10-3C) 1.05x10-1D) 6.40E) 3.91x102Practice ProblemCH110 FA11 SAS 6N2(g) + 3H2(g) 2NH3(g)In the Haber-Bosch process above, what is the estimated ΔHrxnbased on the bond enthalpies shown below?H - H = 432 kJ/molN - H = 391 kJ/molN - N = 160 kJ/molN = N = 418 kJ/molN ≡ N = 941 kJ/molA) -890 kJ/molB) -632 kJ/molC) -109 kJ/molD) 892 kJ/molE) 1064 kJ/molLe Châtlier and Haber-BoschCH110 FA11 SAS 7N2(g) + 3 H2(g)2 NH3(g)cat.• Less moles of product gas than reactant• Remove product from reaction mixture• Exothermic reaction (heat is product)The Problem: it takes a LONG time for the reaction to reach equilibrium at low tempThe Solution: Use a catalyst (Fe and metal oxides) optimum temp is 400 – 500 oC, P 200-600 atmHow can we increase NH3 production?In this reaction there are:How Fast is Equilibrium Reached?CH110 FA11 SAS 8The equilibrium position (Keq) tells us ________ about how fast equilibrium will be reached from a given set of conditions. N2(g) + O2(g) 2NO(g) K ~10-30So, 2NO(g) N2(g) + O2(g) K ~1030BUT, NO(g) ________ at room temperature.What DOES affect equilibrium?concentrationvolume (if gases are involved)temperature (changes the value of Kc)What DOES affect the rate of a reaction?Catalysts, Equilibrium, and RatesCH110 FA11 SAS 9• Catalysts _______consumed during the reaction• Increases the _____ at which equilibrium is achieved• _______ change KeqDemo: Peroxide DecompositionCH110 FA11 SAS 102 H2O2(l) → 2 H2O(l) + O2(g) ∆Hrxn= -196 kJ/molKeq= 3.0 x 1020@ 25oCWe have seen this reaction in multiple demonstrations and Keqfavors ________Bottles of aqueous hydrogen peroxide solution are commonly used as a disinfectant, so it must be relatively stable.Metals in your blood catalyze the decomposition of H2O2in your wound.… in Chem 110 we can catalyze the decomposition reaction with MnO2.Thermite Revisited…CH110 FA11 SAS 11Name the type of reaction:What is ΔHofor the thermite reaction shown above?ΔHof= -822.2 kJ/mol for Fe2O3(s)ΔHof= -1669.8 kJ/mol for Al2O3(s)2AI(s) + Fe2O3 (s) → 2Fe(s) + Al2O3(s)A. 847.6 kJ/molB. -847.6 kJ/molC. 2492 kJ/molD. -2492 kJ/molE. Can’t be determinedPhosphorusCH110 FA11 SAS 12Which of the following reactions involving phosphorus is a redox reaction?P4(s) + 5O2 (g) → P4O10(s)P4O10(s) + 6H2O (l) → 4H3PO4(aq)3Ca2+(aq) + 2PO43-(aq) → Ca3(PO4)2(s)CaO(s) + H3PO4(aq) →CaHPO4(aq) + H2O(l)3Ca3(PO4)2(s) +6H2SO4(aq) →6CaSO4(aq) + 3Ca(H2PO4)2(aq) A.B.C.D.E.Dietary CalciumCH110 FA11 SAS 13Cows milk contains 300 mg of calcium in the form of Ca3(PO4)2per 240 mL serving (The FDA recommends 1000 mg calcium /day for adults). If the solubility of tricalciumphosphate in water is about 0.0020 g/100 mLat room temperature, how much Ca2+(aq) is available in a glass of milk?0.78 mg1.9 mg4.8 mg12 mg190 mgA.B.C.D.E.Dietary CalciumCH110 FA11 SAS 14Tricalcium phosphate [ Ca3(PO4)2 ] from cow’s milk reacts with hydrochloric acid in the stomach, yielding bio-available calcium:What is the equilibrium constant expression for this reaction?Ca3(PO4)2(s) + 2HCl(aq) Ca(H2PO4)2(aq) + 2CaCl(aq)What You Should Know CH110 FA11 SAS 15Le Chatlier’s Principle• How does Q help us to predict the direction in which a reaction will proceed?• What drives a system to return to equilibrium when it has been disturbed?• What happens to a system when the concentration of reactants or products is increased or decreased?• What happens to a system when the volume is changed?• What happens to a system when the temperature is changed?Catalysts• Do catalysts change the position of equilibrium? Why or why not?• Is equilibrium generally reached quickly?• How do catalysts change the rate at which equilibrium is achieved?Final Concepts You Should Know:CH110 FA11 SAS 16• How do I balance a chemical equation?• What is the percent yield of a reaction?Chapter 3: Chemical EquationsChapter 4: Chemical ReactionsChapter 5: Thermochemistry• What are precipitation reactions?• What are metathesis reactions? • What are redox reactions in particular and what are oxidation numbers?• What are net ionic


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PSU CHEM 110 - Chemical Reactions Equilibrium Part 4

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