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TAMU CHEM 120 - Clicker questions

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Clicker Questions CHEM 120 (Bethel) 2020 EXAM 1 1) The concentration of acetic acid (MM=60.05 g/mol) in vinegar is 5.0% by mass (the rest can be assumed to be water). What is the molality? a. 0.83 m b. 0.88 m c. 5.2 m d. 0.083 m e. 5.0 m 2) Calculate the Solubility of O2 in 25.0 °C water at a partial pressure of 120 torr, given that kn=1.3 x 10-3mol/L atm for O2 at 25.0 °C? a. 2.05 x 10-4 M b. 2.1 x 10-4 M c. 0.16 M d. 0.156 M e. 3.9 M 3) The osmotic pressure of an aqueous solution of Cobalt (II) Bromide is found to be 0.674 atm at 75 °C. Calculate the concentration of the salt. a. 0.0275 M b. 0.00915 M c. 0.00783 M d. 0.0236 M e. 0.0100 M 4) A solution is prepared by dissolving 0.131 g of a molecular substance in 25.4 g of water, kFP = -1.86 °C. If the solution has a freezing point of -0.104 °C. What is the molecular mass of the substance? a. 131 g/mol b. 251 g/mol c. 3.12 g/mol d. 92.1 g/mol e. 53.2 g/mol 5) What is the rate law for the following reaction? BrO3 (aq) + 5Br (aq) + 6H+ (aq) -> 3Br2 (aq) +3H2O (aq) Note that this reaction is first order in both BrO3 and Br, and fourth order overall? a. Rate = k[BrO3-][Br-][H+] b. Rate = k[BrO3-][Br-][H+]2 c. Rate = k[BrO3-][Br-]5[H+]6 d. Rate = k[BrO3-][Br-] e. Rate = k[BrO3-][Br-][H+]4 6) Rate data were obtained at 25 °C for the following reaction . What is the rate law expression for this reaction? A + 2B -> C + 2DExperiment Initial [A] (M) Initial [B] (M) Rate of C (M/s) 1 0.10 0.10 3.0 x 10-4 2 0.30 0.30 9.0 x 10-4 3 0.10 0.30 3.0 x 10-4 4 0.20 0.40 6.0 x 10-4 a. Rate = k[A][B] b. Rate = k[A][B]2 c. Rate = k[A]2[B] d. Rate = k[A] e. Rate = k[B] 7) The rate of decomposition of chemical P was measured and a linear fit was for for ln [P] vs. t. The best fit line has the equation y = -0.0217x – 6.2146. What is the rate law? a. Rate = 0.0217[P] b. Rate = 0.0217[P]2 c. Rate = -0.0217 d. Rate = -0.0217[P] e. Rate = -0.0217[P]2 8) Sucrose decomposes to form fructose and glucose in an acidic solution with the following rate law. Rate = k[C12H22O11] and k = 0.216 hr-1 at 25.0 °c. What is the amount of time required for an initial concentration of 0.449M to decompose to 0.0561? a. 0.216 hours b. 0.648 hours c. 3.21 hours d. 4.61hours e. 9.63 hours 9) The rate law of a reaction is Rate = k[NOBr]2. If the half life for this reaction is 2.00 s when [NOBr]0 = 0.900 M. How long will it take to decrease the concentration of NOBR to 0.010 M? a. 0.35 s b. 0.56 s c. 4.0 s d. 13 s e. 180 s 10) Dinitrogen Tetroxide decomposes to nitrogen dioxide and the following rate constants were determined at varying temperatures. k1 = 4.5 x 103 s-1 T1 = 25.0 °C k2 = 1.5 x 104 s-1 T1 = 25.0°C What is the activation energy? a. 2.00 x 10-4 kJ/mol b. 0.751 kJ/molc. 20.8 kJ/mol d. 7.51 x 102 kJ/mol e. 2.08 x 10-4 kJ/mol 11) A reaction generates Hydrazine from Ammonia and Hypochlorate according to the following proposed mechanisms. Step 1 (Fast): NH3 (aq) + OCl-(aq) -> NH2Cl(aq) + OH-(aq) Step 2 (Slow): NH2Cl(aq) + NH3 (aq) -> N2H5+(aq) + Cl- (aq) Step 3 (Fast): N2H5 (aq) + OH- (aq) -> N2H4 (aq) + H2O (aq) Which of the following is TRUE? a. The overall reaction is NH3 (aq) + OCl- (aq) -> N2H4 (aq) + Cl-(aq) b. Step 1 is rate determining c. The rate equation for step 2 is Rate = k2[NH3]2[Cl-] d. NH2Cl is a reaction intermediate e. H2O is a reaction intermediate 12) What is the mole fraction of NaCl in an aqueous solution (density = 1.20 g/mol) that is 2.5 molal Sodium Chloride? (MM = 58.44 g/mol) a. 0.15 b. 2.6 c. 2.3 d. 0.045 e. 0.043 13) What does this graph indicate? a. Zero-order rate law b. First-order rate law c. Second-order rate law d. Activation energy e. None of the above Answer key: B, B, C, D, B, D, A, E, C, D, E, A, B EXAM 2 1) For the reaction: 2NO2 (g) ⇌ N2O4 (g) If the equilibrium concentrations are NO2 = [1.50 M] and N2O4 = [10.7 M], what is the equilibrium constant? a. 4.76 b. 0.210 c. 0.140 d. 7.13 e. 16.1 2) Kp for the decomposition of nitrogen dioxide gas into nitrogen monoxide and oxygen gas is 6.3 x 10-13 at 25°C. What is Kc? Hint: remember the first step is always a balanced chemical equationa. 1.6 x 10-9 b. 6.3 x 10-13 c. 1.5 x 10-11 d. 2.6 x 10-14 e. 2.5 x 10-16 3) PCl3(g) + Cl2(g) ⇌PCl5(g) K = 33 @ 250.0°C If an experiment has starting concentrations of 0.050 M PCl3 and 0.050 M Cl2, what is the concentration of Cl2 after the reaction has reached equilibrium? a. 0.043 M b. 0.023 M c. 0.027 M d. 0.037 M e. 0.107 M 4) NO(g) is produced during combustion at high temperature according to the reaction. N2 (g) + O2 (g) ⇌ 2NO(g) K = 1.0 x 10-5 at 1500 K If a sample of air has a concentration of 0.080 M N2 and 0.020 M O2, what is the concentration of NO after combustion at 1500 K? a. 0.080 M b. 0.020 M c. 1.6 x 10-6 M d. 6.3 x 10-5 M e. 1.3 x 10-4 M 5) Th water-gas shift reaction is used to produce H2 industrially. CO(g) + H2O(g) ⇌ CO2 (g) + H2 (g) Which of the following conditions will result in the largest increase of the production of hydrogen gas? a. Increasing concentration of CO(g) and CO2 (g) b. Decreasing concentration of H2O(g) and CO2 (g) c. Decreasing concentration of H2O(g) and CO(g) d. Increasing concentration of H2O(g) and CO(g) e. Increasing concentration CO2(g) 6) Which of the following conditions will increase the concentration of the products for the following reaction? N2(g) + 3H2(g) ⇌ 2NH3(g) ΔHf = -46.11 kJ/mol a. Increasing temperature b. Increasing moles of H2 c. Decreasing pressure d. All the above e. None of the above 7) As the number of microstates over which energy can be distributed in a system increases, its entropy a. Decreases b. Increasesc. Remains constant d. Cannot be determined 8) Which of the following reactions should have a ΔSrxn > 0? a. H2O(l) -> H2O(g) b. Ag+(aq) + Cl-(aq) -> AgCl(s) c. 4Al(s) + 3O2(g) -> 2Al2O(g) d. CO(g) + 1/2O2(g) -> CO2(g) e. 2NO2 (g) -> N2O4 (g) 9) Calculate the standard entropy change for the production of one mole of liquid methanol (CH3OH) from carbon monoxide gas and hydrogen gas. a. -331.9 J/K mol CH3OH(l) = 127.2 J/K mol b. 331.9 J/K mol CO(g) = 197.7 J/K mol c. -201.2 J/K mol H2(g) = …


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