Practice+Exam+1_A_+Key

Practice+Exam+1_A_+Key - Part I Multiple Choice Concept and...

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Unformatted text preview: Part I: Multiple Choice, Concept and Short Calculations, 135 pts - No Partial Credit l.( 10 pts) When a reaction takes place where the products have a higher energy than the reactants, a) the energy of the system increases. C9 the reaction is endothermic. c) energy is released. d) work is done by the system. e) the reaction is exothermic. 2.( 10 pts) When ice melts at constant pressure, the sign of the enthalpy change for the process a) depends on the container volume. b) is negative. 0) depends on the temperature. (cl—y is positive. e) cannot be determined. 3.( 10 pts) Consider the heating curve for one mole of a substance that melts at —23°C and boils at 327°C. 800 700 TIK 2000 100 100 300 400 5m 6w run 800 900 Us The horizontal portion of the heating curve at 600 K represents the l a) } enthalpy of vaporization of the substance. b) enthalpy of sublimation of the substance. c) heat required to bring the substance to its melting point. (1) heat required to bring the substance to its boiling point. e) enthalpy of fusion of the substance. CAM 9% 55,2; , My; 54,”; (a, {.y 2 4.(15 pts) A piece of aluminum of mass 12.0 g at 950°C was placed in a calorimeter that contained 100.0 g of water at 250°C. If the temperature of the water rose to 27°C, what is the specific heat capacity of aluminum? The specific heat capacity of water is 4.18 J "C'1 g‘1. J a) 0.73 0C g b) 4.6 ocg c)7.6 J a [72.0% (3/; ,4; "L (/7‘?527: Mflrt éé/W‘Rfl OCg d) 4.1 J /&0 A 44/? 2t .20 10212-68 ng (5/34, ': 5.(10 pts) The boiling point of HBr is higher than HCl due to a) hydrogen bonding. b) dipole-dipole forces. 0) ion-dipole forces. d) ion-ion forces. London forces. 6.(10 pts) The meniscus of ethanol curves upward in a glass tube forming a "U" shape. This means a the cohesive forces between ethanol molecules are not as strong as the adhesive forces between ethanol and glass. b) the cohesive forces between ethanol molecules are stronger than the adhesive forces between ethanol and glass. c) ethanol has a high surface tension. d) ethanol has a small capillary action. e) ethanol tends to cover the smallest possible area of the glass. Key 3 7.(10 pts) An animal cell assumes its normal volume when it is placed in a solution with a total solute molarity (molarity of nonelectrolytes plus ions) of 0.3 M. If the cell is placed in a solution with a total solute molarity of 0.15 M, a the escaping tendency of water in the cell increases. a water enters the cell causing expansion. c) water leaves the cell causing contraction. (1) no movement of water takes place. 6) the escaping tendency of water outside the cell decreases. 8.(15 pts) Calculate the vapor pressure of an aqueous solution containing 100.0 g sucrose (molar mass, 342.3 g-mol—l) dissolved in 200 g water (molar mass, 18.0 g-mol‘l) at 100°C. a) 20 Torr /00 f :- o, 27;? MID/ac sac. 740 Torr 5 9’2; 3 c) 290 Torr / 200 7/ d 40 T .___. \ ) 0” A bro/(5 /,10 e) 650 Torr /310 Pvflf ; XSJiflr * 9.(15 pts) Ethanol is often promoted as an alternative to petroleum fuels. Given the standard enthalpies of formation of C02(g) [—394 kJ-mol—l], H20(l) [—286 kJ ~mol—1], and ethanol, C2H50H(l), [—278 kJ/mol], and the balanced reaction for combustion of ethanol: C2H50H(l) + 3 02(g) —> 2 C02(g) + 3 H200) calculate the standard enthalpy of combustion of 1 mole of ethanol. a) —402 k] D b> aim/AZ (can 3%A//,(/é0) I M; cal/row c) -2,624 k] d) —1,368 k] e) —958 kJ 10.(15 pts) Which of the following compounds would require the highest applied pressure to obtain pure water by reverse osmosis? . . a I“ 771‘ L M )6 7 a) 1.0MA1C13 41* /: 4 s: b) 2.0 M BaC12 3* 2:( c) 2.0 M sucrose )x 2 r 2 d) 2.0MNaCl U2 24 e) 1.0 M CuC12 IA‘ 5 = 3 11.(15 Points) A calorimeter was calibrated by carrying out a reaction which released 15.6 k] of heat. If the temperature of the calorimeter rose 3:25°C, what is the heat capacity of the calorimeter? k] a) 8.37 o C / 9 r A K 3’ X j b) 4.80 {‘1 o I 4, 30 ___,__ 3, ,2 § C ac c) 2.58 g d) 24.0 EC]: 6) 0.96 3% 7%” 1y Part 11: Show work for partial credit (115 points) 12.(40 Points) Geothermal energy sources include such things as natural steam vents. The energy (heat) stored in the water vapor can be used for other purposes and reduce the need to burn hydrocarbons. Calculate the energy liberated by cooling 18 grams of water vapor at 160°C to liquid water at room temperature (25°C). cS (water ice)=2.03 o—J— cS (liq. water)=4.l8 o—L cs (water vapor)=2.01 3]— P C g P C g P C g AH§US(H20) = 6.01 kJ/mol AH‘V’ap(H20) = 40.7 kJ/mol Mo ‘2 ® 3: Mat- Cf/fl/ m5”, 7K AT 0( @ W 3) @ : My! 2,o/ x ‘ (Mo-Ago) T'Z./?*/o; 3’ @ zr~m¥ AHW 1“(1,0 *1 Magi * r—ma KJ’ :- Wan/a3; l3.(35 Points) Given the following heats of reaction: a 2 C2H2(g) + 5 02(g) —> 4 C02 + 2 H20(l) AH°=-2,600 kJ @ C6H6(l) + 15/2 02(g) -> 6C02 + 3H20(l) AH°=-3,268kJ calculate the reaction enthalpy for C6H6(l) —> 3C2H2(g) Show all work. 3 Mid/i. M21 (D Jay ‘/‘2 5502(9) 7‘ 3/éfl/«O "'7 125’ 02/3) + 3 (242/3) Alfl‘fa/vacfir 9”! ‘0 * W (Mg/e) -> 39 #2 (3) AM} + 432 M7 + fly 6 l4.(40 Pts) The osmotic pressure of 250 mg of the protein carbonic anhydrase (a large biomolecule) dissolved in enough water to give 25.0 mL of solution is 6.20 Torr at 25°C. Calculate the molar mass of carbonic anhydrase. 7f: cl M X 7— Molar mass : i Mo/ fifihm Z: I __ 77' 4,20 72r/A m ~ K : ('7‘6/4 7 {2,3437}? 76 293K : Bee/,1 /a‘4 21:21 (9,250 3 4/ W 27 W0 .2 ...
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