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Final Exam Jeopardy

Final Exam Jeopardy. Thermo- Chemistry ( D H). Solutions. L iquids & S olids. B onding Part II. G ases. c hemical R eactions. 500. 500. 500. 500. 500. 500. 400. 400. 400. 400. 400. 400. 300. 300. 300. 300. 300. 300. 200. 200. 200. 200. 200. 200. 100. 100.

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Final Exam Jeopardy

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  1. Final Exam Jeopardy

  2. Thermo- Chemistry (DH) Solutions Liquids & Solids Bonding Part II Gases chemical Reactions 500 500 500 500 500 500 400 400 400 400 400 400 300 300 300 300 300 300 200 200 200 200 200 200 100 100 100 100 100 100 Final Jeopardy Question

  3. Thermochemistry 500 pts You dissolve 65 grams Li2S in 195 mL of 31°C water. After dissolving, the temperature of the solution is 20°C. A) what is DHsoln Li2S, including the correct unit and sign, +/-, and B) what is the system and what is the surroundings, and C) is the process exothermic or endothermic? DHwater = (195 g)(-11°C)(4.18 J/g°C) = -8966.1 J This is the energy change of this specific process, but DHsoln is the energy change permol, so divide the energy change by the amount of moles: +8966.1 J = +6331 J/mol = DHsoln Li2S 65 g /45.9 g/mol Note that the sign changes due to it being endothermic from the system point of view. Why do you supposeDHsoln is expressed per mol? Back

  4. 4 1 2 3 r x n p r o g r e s s Thermochemistry 400 pts Label each of 1-5; explain what is occurring in 2, explain what 4 and 5 are. In the nails lab, how did the aqueous copper ions become copper metal and why did the color change from blue to (copper) brown? 5 • Energy of reactants, 2) energy released by the reaction, DH, 3) energy of products, 4) energy of activation, EA: energy required for the reaction to occur, 5) activation complex: single particle formed by colliding reactants existing momentarily. Back

  5. Thermochemistry 300 pts For the reaction If DHrxn = -0.85 kJ, 1) What mass of magnesium will produce 6500 joules of energy? 2) Rewrite the reaction with the energy term as part of the reaction 3) Is the reaction endothermic or exothermic? Mg(s) + Au2(SO4)3(aq) MgSO4(aq) + Au(s) 3Mg(s) + Au2(SO4)3(aq) 3MgSO4(aq) + 2Au(s) + 0.85 kJ 24.3 g Back

  6. Thermochemistry 200 pts You add 0 °C ice to 25 cm3 of 48 °C water. What mass of ice will cool the water to 41 °C? Additional info: Cliquid H2O = 4.18 J/g °C, Cice = 2.1 J/g °C, DHfus = +6.01 kJ/mol DHice = DHwater (X g ice/18 g/mol)(6010 J/mol) = (25 g)(7°C)( 4.18 J/g °C) X = 2.19 g ice Back

  7. Thermochemistry 100 pts You run out of water during your summer trip to Isla Grevy. It’s -38 °C outside. You break off some surface ice and your scale tells you it is 2480 grams. What amount of heat energy will you need to warm it up to 30 °C? ADDITIONAL INFO:Cliquid H2O = 4.18 J/g °C, Cice = 2.1 J/g °C, DHfus = +6.01 kJ/mol Answer = 1,343,967 J = 1344 kJ (38)(2480)(2.1) + (2480/18)(6010) + (30)(2480)(4.18) 30 DH2 DH3 DT2 0 Back DT1 DH1 -38

  8. Solutions 500 pts You have a solution of zinc chloride and you need to precipitate out the cation. What compound could you use? Write the complete balanced reaction with states included. Any soluble compound that contains any of the following anions: carbonate, hydroxide, phosphate, sulfide, sulfite, As long as its cation does NOT precipitate chloride—then you would have two precipitates! Back

  9. Solutions 400 pts Which of the following will dissolve in a non-polar solvent? Explain your reasoning. a) CHCl3 b) BCl3 c)NF3 d) HF a, c, and d are polar, b is non-polar: a is symmetrical but has different outside atoms; c is not symmetrical and so the polarity of its bonds do not cancel; d is not symmetrical and so the polarity of its bond does not cancel; b is trigonal planar, and therefore the polarity of the B-Cl bonds cancel, so it is non-polar and will therefore dissolve in a non-polar solvent. Back

  10. Solutions 300 pts What is DTfp when dissolving 55 g sodium sulfite in 555 cm3 of water? for Na2SO3, i = 3 DT = imKfpm = molality = mols solute/kg solvent Back

  11. Solutions 200 pts 1) What is the difference between being on the solubility line and above the line? Assume no supersaturation has occurred! 2) You have 200 mL of a saturated solution of ammonium chloride at 30 °C. What mass of solute must be added to saturate it if the temperature is raised to 50 °C? 1) If the solution is on the line, then the maximum amount of solute is dissolved, so it is saturated but there is no undissolved solute. Above the line, it is still saturated, but because there is more than the maximum amount, there is undissolved solute, and a dynamic equilibrium is established: dissolved solute joins the undissolved solute, while undissolved solute becomes solvated. This occurs at the same rate, and so the amount of dissolved and undissolved remains constant. 2) Solubility at 30°C = 82 g/200 g H2O. Solubility at 50°C = 102 g/200 g H2O. 102 – 82 = 20 grams must be added to keep it saturated at the higher temperature. Back

  12. Solutions 100 pts In general, what is the minimum size of particles considered to be a colloid? It must be > 1 nm, which is large enough to reflect light, which creates a Tyndall beam. Back

  13. L & S 500 pts What makes the slope of water’s solid-liquid equilibrium line interesting? Lots ‘o stuff…. Back

  14. L & S 400 pts Draw two kinetic energy distribution curves of two samples of a substance at two different temperatures. Assume that each sample has the same amount of particles. Label which is warmer, which is colder A and B represent the two average kinetic energies. B > A, so the red temperature is greater than the blue temperature. Same amount of particles in both means the area under each curve must be equal. Back

  15. phase diagram of iodine L & S 300 pts 1) At normal pressure and room temp, what would happen to solid solid iodine if the temperature was was raised by 50 °C? 2) Under what conditions could you expect iodine to exist as a liquid? Normal P = 1 atm, room temp = ~25 °C. A 50 °C increase would be ~75 °C. At 25 °C and 1 atm, I2 is a solid, at 75 °C I2 is a gas, so it will sublimate. Iodine exists as a liquid under conditions of T and P indicated by the greenish shaded area on the graph. Back

  16. L & S 200 pts The table at right gives various vapor pressures for water at various temperatures. The vapor pressure increases with temperature. Would you expect this to be the case with any liquid? Explain. Vapor pressure of water Temperature Pressure (̊C) (mmHg) 10.0 9.2 20.0 17.5 30.0 31.8 40.0 55.3 50.0 92.5 60.0 149.4 70.0 233.7 80.0 355.1 90.0 525.8 100.0 760.0 As can be seen by the graph from the answer to Liquids & Solids-400 pts, as KE increases, more and More particles have enough energy to break away from the liquid and become a gas. Since it is the vapor (gas) particles that create vapor pressure, the more vapor given off by the liquid, the higher the vapor pressure will be. Back

  17. L & S 100 pts Liquid nitrogen (bp = -194 °C) is used by physicians to kill unwanted cells on the skin (warts, pre-cancerous tissue, etc.) by freezing the cells. Why would freezing a cell kill it? Would you expect it to just thaw back to its pre-frozen state? Is it possible to have one substance be a solid and another substance be a gas if they have same KE? Explain. Since water expands when it freezes, the expanded water (ice) will burst the cell, thus killing it. Back

  18. Bonding part II 500 pts What is the hybridization of nitrogen’s valence electrons in the molecule at right? Draw using arrows and boxes, include the name(s) of the orbital(s); AND name the shape at the nitrogen and at the carbon! H H—C=N—H Nitrogen has 5 valence e—. It has three bonds, one pi and two sigma, and one pair of unbonded electrons. Electrons in pi bonds come from unhybridized p-electrons, so one of nitrogen’s p valence e— remains unhybridized so it can pi-bond to carbon. The rest of the e— are hybridized as shown above. SHAPES: Since N has one pair of unbonded electrons, that pushes the bonds out of line and it is therefore bent. Carbon has three electron groups around it, all bonded, so they spread out in a trigonal planar shape. Back

  19. bonding part II 400 pts Of the two molecules pictured below, C2H6 (ethane) and H2CO (formaldehyde), which would need more kinetic energy to break away from its liquid state and become a gas? (both are 30 g/mol) Explain your answer. Water has a very low molar mass; Why is it a liquid at room temperature rather than a gas? The shape and bond polarities of formaldehyde give it a strong dipole. Ethane is completely symmetrical and non-polar. The stronger dipole- dipole interactions of formaldehyde would require greater energy to break away from the liquid. Back

  20. bonding part II 300 pts Is the compound at right polar or non-polar? Explain your reasoning! Are there any unbonded electron pairs on this central atom? Explain how you know. (hint: each bond is a single bond) What is its VSEPR shape? Would you expect it to be a polar molecule? Without an unbonded pair on the central atom, the shape would be trigonal planar. Here, the bonds have been pushed out of the plane, so there must be an unbonded pair repelling the bonds. The shape is pyramidal. Pyramidal is not symmetrical, and so IF the bonds are polar, then the molecule would be polar as well—the bond polarities would not cancel due to the non-symmetrical shape: the polarity vectors of the bonds would not add up to zero. Back

  21. Bonding II 200 pts How many p-bonds are in C3H4? Show the dot and dash structure—the carbons are in the middle. H H C=C=C H H There are two double bonds, each has one pi and one sigma, so there are a total of two pi bonds. Back

  22. Bonding II 100 pts Is the compound at right polar or non-polar? Explain your reasoning! Why do atoms form bonds? Water has the lowest mass of any molecule except hydrogen; Why is it a liquid at room temperature rather than a gas? The molecule is tetrahedral, which is a symmetrical shape. All outside atoms are the same, so any bond polarity would be cancelled due to the symmetry: the bond polarity vectors would add up to zero. The molecule is therefore non-polar. Back Which of the following will dissolve in a non-polar solvent?

  23. GASES 500 pts For the combustion of 90 grams of ethene, C2H4, What volume of carbon dioxide is produced at 690K and 103 kPa? C2H4 + 3O2 2CO2 + 2H2O 358 Back

  24. GASES 400 pts 3 g of a gas in a 400 mL sealed container are held at 151 K and 1.62 atm. What is the molar mass of the gas? What is the density of a gas with a molar mass of 30 g/mol at 120 kPa and 200 K? Back

  25. GASES 300 pts 25 grams C2H4 is at 300 kPa in a volume of 2500 mL. What is it’s temperature? Back

  26. GASES 200 pts A balloon originally at 500 torr, 30 °C, and 35 mL, changes to 400 torr and 40 mL. What would the temperature be under the new conditions? 277 K Back

  27. Gases 100 pts The two balloons at right are at the same T and P, their volume ratio is 5:9. What relationship among the four gas variables gives you that volume ratio? Volume, V, is directly proportional to the amount of particles, n, when T and P are held constant. Back

  28. reactions 500 pts What is the molar mass of Pb3P4? What is the mass of 6.02 x 1023 particles of Pb3P4? What is the mass of 1 mole of Pb3P4? What is the mass of 1 mole of Pb3P4 formula units? For the reaction of aluminum with aqueous copper II nitrate, what is • The oxidation 2Al  2Al3+ + 6 e- • The reduction 3Cu2++ 6 e- 3Cu C) The oxidizing agent Cu2+ D) The reducing agent Al • The number of electrons exchanged in the balanced equation 6 2Al + 3Cu(NO3)2 2Al(NO3)3 + 3Cu For the reaction Given the density of gold = 19.5 g/cm3, and the concentration of Au2(SO4)3 = 0.5 M, What volume of AuSO4(aq) is required to produce 25 cm3 of gold? Mg(s) + Au2(SO4)3(aq)--> MgSO4(aq) + Au(s) Back

  29. reactions 400 pts For the reaction ZnF2(aq) + AlCl3(aq) What minimum mass of ZnF2 solid must be dissolved in 555 mL of 0.666 M AlCl3 to react completely? For the reaction Mg(s) + H2O(l) Mg(OH)2(aq) + H2(g) the total volume of the reactants is 550 mL. If 1.5 g Mg reacts completely, then what is the molarity of the aqueous product, assuming no change in volume occurs during the reaction? 3ZnF2(aq) + 2AlCl3(aq) 3ZnCl2(aq) + 2AlF3(s) Back

  30. reactions 300 pts In a combustion reaction, 22 g ethene, C2H4, reacts with 52 grams oxygen. Which is limiting? C2H4 + 3O2 2CO2 + 2H2O needed have The fire in the halloween demo came from the combustion of glycerin, C3H8O3. Write and balance the equation for the combustion of glycerin. 75.4 g oxygen is needed to react with 22 g ethene, but there are only 52 g oxygen available, so oxygen is limiting. Back

  31. reactions 200 pts For the reaction Mg(s) + H2O(l) Mg(OH)2(aq) + H2(g) what volume of hydrogen gas is produced from the reaction of 500 grams water in excess magnesium at STP? Back

  32. reactions 100 pts Write the net ionic equation for the following reaction K2CO3(aq) + ThCl4(aq) KCl(aq)+ Th(CO3)2(s) Balance the following: KClO3 + C4H8 CO2 + H2O + KCl Ionic: 4K++ 2CO32- + Th4+ + 4Cl-  2K+ + 4Cl- + Th(CO3)2(s) Net ionic: 2CO32-+ Th4+ Th(CO3)2(s) Back

  33. What is the basis for Avogadro’s Number? Final Jeopardy What two units used in chemistry are derived from carbon-12, and how are they derived? Time is up! You have 15 sec! Back

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