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UT CH 302 - Final Exam Study Guide

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CH 302 1st EditionFinal Exam Study Guide: Lectures: 1 - 27Thinking like a ChemistLecture 11. Enthalpy- Enthalpy is related to the energy of a substance- Liquids have a lower enthalpy than gases because it has a lower energy and stronger IMFs, so it is more stable2. Entropy- Entropy increases with:o Increasing volumeo Increasing temperatureo Going from a solid to liquid to a gas3. Gibb’s Free Energy- At equilibrium delta G = 0 and H = TS- The difference in boiling point result from the differences in IMF- The stronger the IMF, the bigger the enthalpy, the higher the temperaturePractice Problems:1.The change in free energy for the given reaction is −1 kJ/mol at room temperature. What is the equilibrium constant for the reaction at the same temperature? (R = 8.3 J · K−1mol−1)A. 1.5B. -1.3C. 3D. 0.01E. 1.02. Consider the following statements. Which are true?I) Vapor pressure is an equilibrium phenomenon.II) The smaller the IMF, the smaller the vapor pressure.III) The volume of a liquid does not affect the vapor pressureIV) Vapor3. Which of the following is a possible combination of values for ∆Hlattice, ∆Hhydration and ∆Hsolution, respectively, for a salt whose dissolution is endothermic?A. −900, −900, and − 1800 kJ · mol−1B. +550, −480, and + 1030 kJ · mol−1C. +640, −620, and + 20 kJ · mol−1D. −450, +400, and − 50 kJ · mol−1Answers:1.A2. I, III, and IV3. CPhase ChangesLecture 2- Vapor Pressureo Vapor pressure and delta H of vaporizationare inversely proportional (as VP increases,DH decreases)o Vapor pressure is dependent on To Vapor pressure is independent of the amountof liquid presento The stronger the IMFs, the bigger thedifference the liquid and the gas, the largerthe DH and the lower the VP- Phase Diagramo Normal phase changes occur at 1 atm, but phase change temperatures vary with pressureo Phase changes are an equilibrium conditiono You can refer to a phase diagram to determine at what phase a particular substance will be in based on the external pressure and temperaturePractice Problems:1. In general decreasing the temperature makes which phase transitions more likely to occur?A. Condensation, freezing, depositionB. Evaporation, deposition, freezingC. Sublimation, condensation, freezingD. Evaporation, fusion, sublimationE. Condensation, fusion, deposition2. According to the given phase diagram for carbon dioxide,what are regions 1, 3 and B respectively?A. solid, liquid, triple pointB. solid, vapor, triple pointC. solid, liquid, critical pointD. solid, vapor, critical pointE. liquid, vapor, critical pointAnswers: 1.A2.DDissolutionLecture 31. What is going on with the entropy of dissolution?- The entropy always increases - The entropy of a solution is usually easy to predict- Solutions typically have higher entropy than the unmixed compounds2. What is the free energy change for gases mixing?- Delta G is negative, therefore it is spontaneous3. Why does the free energy decrease?- Delta H is zero and Delta S is positive- G = H – TS- Therefore this means that spontaneous dissolution must be entropically driven4. What is the sign for the change in free energy for the dissolution process in which polystyrenepeanuts were placed in water?- Positive because the process was nonspontaneous5. What is the sign for the change in entropy for the dissolution process in which polystyrene were placed in acetone?- Positive6. What is the sign for the change in enthalpy for the dissolution process in which biodegradablepeanuts were placed in acetone?- Positive because G is positive and S is positive (G = H – TS)Solution PropertiesLecture 4- Thermodynamics of Solutionso An increase in temperature drives to greater solubility because the free energy ofsolution is lowero Delta H of a solution for a gas is negative (exothermic)o In reality, things always dissolve just a little tiny bito Instead we should ask about what the magnitude of G is, the bigger the negative number the greater the solubility- When adding water and salt to form salt water, which has the higher entropy the solution or the water + solid salt separately?o The solution because there are more microstateso They have the same enthalpy because DH is about 0o The solution has a lower free energy - Colligative propertiesEffects of making the solution:o Solution now more stable than vapor, therefore boiling point goes upSolution now more stable than solid, therefore freezing point goes down- Colligative properties depend on the concentration of a solute NOT the type of solute- Colligative properties are:o Vapor pressure loweringo Boiling point elevationo Melting point depressiono Osmotic PressurePractice Problems:1. Which of the following statements regarding colligative properties is/are true?I) Pure liquid water exhibits a lower freezing point than a solution of magnesium chloride in water.II) For completely soluble compounds that do not ionize in solution, the van’t Hoff factor, i = 1III) Osmotic pressure is pressure exerted on a semipermeable membrane between solutions with different concentrations of solutes.2. Assuming all of the following salts dissolve completely in water, which one would be the best to use if you were trying to raise the boiling point of the solution?A. Na3PO4B. Al2(SO4)3C. KNO3D. (NH4)2Cr2O7E. NaClAnswers:1.II, III2. BSolubility EquilibriumLecture 5- Concept of SolubilityWhat is the molar solubility of CaCl2?1. Write the formula equation down: CaCl2 (s)  Ca2+ (aq) + 2 Cl- (aq)2. Given g solute/ 100 g H2O (solvent), we now have 64.7 g solute/ 164.7 g solutiono Solution = solvent + solute so 100 g H2O (solvent) + 64.7 g solute = 164.7 g solution3. Dimensional analysis to achieve moles/L64.7 g CaCl2 x 1 mole CaCl2 x 1.435 g CaCl2 solution x 1000 mL = 5.08 moles/L164.7 g soln. 111.07 g CaCl2 1 mL solution 1 L- Solubility Rules:1. All common compounds of Group I and ammonium ions are soluble. 2. All nitrates, acetates, and chlorates are soluble. 3. All binary compounds of the halogens (other than F) with metals are soluble, except those of Ag, Hg(I), and Pb. Pb halides are soluble in hot water.) 4. All sulfates are soluble, except those of barium, strontium, calcium, lead, silver, and mercury (I). The latter three are slightly soluble. 5. Except for rule 1, carbonates, hydroxides, oxides, silicates, and phosphates are insoluble. 6. Sulfides are insoluble except for calcium,


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UT CH 302 - Final Exam Study Guide

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