Chem 5 Fall This reaction is a (circle ONE) (2) Acid-Base Reaction Precipitation Reaction Redox Reaction

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Hilda Mills
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1 1. (16) Draw Lewis structures for FOUR of the following molecules or ions. Include all important resonance forms. Clearly label EVERY atom with its formal charge. The FIRST eight structures that you write will be graded, unless you cross out molecules or ions that you do not want to be considered. SF 4 PF 5 NO 2 XeF 2 SCN

2 2. In artificial atmospheres, like submarines and spaceships, exhaled carbon dioxide can be converted to oxygen using postassium superoxide, KO 2, according to the following reaction: KO 2 (s) + CO 2 (g) K 2 CO 3 (s) + O 2 (g) (6) Calculate the mass of KO 2 needed to react with 50.0 L of carbon dioxide at 25ºC and 1.0 atm. (4) Calculate the volume of O 2 gas produced under these conditions of temperature and pressure. This reaction is a (circle ONE) (2) Acid-Base Reaction Precipitation Reaction Redox Reaction The results of this problem illustrate (circle ONE) (2) Boyle s Law Law of Combining Volumes Dalton s Law

3 3. Multiple Choice Evaluate each choice carefully. There may be more than one correct response! (3) The container represented below contains 1.00 g of H 2 gas. Freely-moving piston 1.00 g H2 (g) at P atm The container is kept at constant atmospheric pressure by a freely moving piston. If 1.00 g of He is added to the above cylinder, circle the sketch below that is the best representation of the resulting gas mixture. Assume the gas remains at constant temperature and atmospheric pressure. A. B. C g H 2 (g) g He (g) 1.00 g H2 (g) g He (g) 1.00 g H 2 (g) g He (g) (4) A sample of gas is trapped in the sealed end of a J-tube manometer containing liquid mercury, as shown below. P atm If additional mercury is added to the open end of the tube, which of the following statements will be true? Hg Gas A. The volume of trapped gas will decrease. B. The pressure of trapped gas will increase C. The number of particles per unit volume will increase. D. The pressure of the gas will be greater than atmospheric pressure.

4 More Multiple Choice: There may be more than one correct response! (4) A gas mixture contains 3.0 moles of He, 1.0 moles of N 2, and 1.0 moles of CO 2. The total pressure is 1.00 atm and the temperature is 298 K. Which of the following statements are true, assuming the gases behave ideally? A. On average, the helium atoms are moving with greater speed than the nitrogen molecules and the carbon dioxide molecules. B. The partial pressure of N 2 is less than that of He and equal to that of CO 2. C. On average, the kinetic energy of the CO 2 molecules is larger than that of the He atoms or N 2 molecules. D. The total volume of the mixture is greater than 100 L. (4) Consider the following graph, assuming that curves A, B, and C are for the same gas at different temperatures. Circle all the statements below that are true. number of particles A B C speed A. The temperature for curve C is greater than that of B and of A. B. The temperature for curve A is greater than that of B and C. C. On average, particles represented by curve A are moving faster than those represented by curve B and C. D. For all curves, the probability of a given speed increases as the speed increases. (4) Which of the following are state functions? A. Time required for a Green Flame to move from Student A to Student B. B. Enthalpy C. Work D. Horizontal distance across lab bench from Student A to Student B.

5 More Multiple Choice: There may be more than one correct response! (5) Which of the following statements are true of PRESSURE? A. It can be expressed in units of kg m 1 s 2. B. It is defined as force times distance. C. It is defined as force per unit area. D. It is directly proportional to volume, for one mole of ideal gas at fixed temperature. E. It depends upon the number of particles per unit volume, their speed, and their mass. (5) Equal moles of H 2 (g) and O 2 (g) are placed in a vessel and sparked to initiate the formation of H 2 O (g). Assuming that the reaction goes to completion and forms only gaseous product, how does the final volume compare to the initial volume, if both volumes of gas are measured at the same temperature and pressure? A. V initial = V final B. V initial > V final C. V final = 3/4 V initial D. V initial = 3/4 V final E. Volumes cannot be compared from information given. (4) Which of the following statements are true of bomb calorimetry? A. E = q + w Β. w = 0 C. P is constant D. H is determined directly. (4) Which of the following statements are true of solution calorimetry? A. E = q + w B. w = 0 C. P is constant E. H is determined directly. (5) Which of the following statements are true of temperature? Α. It is an intensive property, independent of the amount of material B. It is an extensive property, dependent on the amount of material. C. It is a measure of the average kinetic energy of particles in the material. D. It is a measure of the total kinetic energy of particles in the material. E. For an ideal gas, volume goes to zero and temperature goes to absolute zero.

6 4. Propane gas, C 3 H 8, is burned as fuel, in furnaces and water heaters. The combustion equation is: C 3 H 8 (g) + O 2 (g) CO 2 (g) + H 2 O (l) (8) Use the thermochemical data given for the reactions below to calculate the enthalpy change per mole of propane burned. C (graphite) + O 2 (g) CO 2 (g) H = kj/mole CO 2 H 2 (g) + 1/2 O 2 (g) H 2 O (l) H = kj/mole H 2 O 3 C (graphite) + 4 H 2 (g) C 3 H 8 (g) H = kj/mole C 3 H 8

7 4. Continued (4) A water heater heats 40.0 gallons of water from 25ºC to 75ºC. What quantity of heat would be required to increase the temperature of this amount of water by this many degrees? (4) How many moles of propane must be burned in the water heater to increase the temperature of the water in the tank by this amount, assuming that the water heater is 100% efficient and all heat from the combustion of propane is used to increase the temperature of the water?

8 5. Consider the bond between boron and fluorine in the substance BF 3. The B-F bond length is m and the dipole moment of the B-F bond is 1.8 Debye. The Pauling electronegativity of fluorine is 3.98 and of boron is (3) From a comparison of the electronegativities of B and F, would you classify the bond as covalent or ionic? (5) What is the percent ionic character of the B-F bond? (4) Draw a Lewis structure of the BF 3 molecule, showing the most likely covalent bonding configuration and label each atom with its formal charge.

Chemistry 111 Syllabus

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