Practice Exam 1 Ch 11, 13, 14 Key PDF

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University of Hawaii at Manoa

Chemistry 162

Professor Gary

Practice Exam I KEY -Chapters 11, 13, 141) Which of these has hydrogen bonding capabilities? (Circle all that apply) CH3OH

CH3OCH3

F2

CH3CH3

(CH3)3N

H 2O

2) Vaporization is a(n) ___________ process. a. Exothermic b. Endothermic c. Difficult d. Quick e. None of these 3) When external pressure decreases which occurs? a. boiling point decreases b. boiling point increases c. temperature increases d. liquids condense e. none of these 4) The triple point on a phase diagram is ________. a. Where the substance exist as both a liquid and a gas. b. Where a super critical fluid begins to form. c. Where a given compound is both a solid and a gas. d. Where all three physical states exist at the same time. e. None of the above 5) Which noble gas has the highest boiling point? a. He b. Xe c. Rn d. Ne e. Ar 6) Rank the 4 intermolecular forces from strongest to weakest: Ion-Dipole Interactions, Hydrogen Bonding, Dipole-Dipole Interactions, London Dispersion Forces (Remember: London Dispersion Forces can sometimes outweigh Dipole-Dipole interactions) 7) Which physical state is compressible? Gas

University of Hawaii at Manoa

Chemistry 162

Professor Gary

8) What are the condensed phases of matter? Solids, Liquids 9) When a solid turns into a liquid, this process is called melting and it is an exothermic/endothermic process. 10) Which of these compounds has the lowest boiling point? H2O, CH3OH, CH3-O-CH3, CH3CH3 (Weakest IMF) 11) Which of these two compounds has the higher boiling point? n-pentane; it has stronger London Dispersion forces because it has higher surface area

12) Name ALL intermolecular forces present in each compound. Then, name the strongest intermolecular force present in each compound. Lastly, determine if the two compounds will be soluble with each other. NH3 London (everything has London forces), dipole-dipole, hydrogen bonding (strongest) CH3CH2COCH3 London (everything has London forces), dipole-dipole (strongest)

13) Would the following compounds be soluble with each other? If the two compounds are soluble, state the strongest intermolecular force responsible for the solubility: a. Water and solid FeCl3: Soluble/Insoluble

Intermolecular Force: Ion-Dipole

b. C8H18, (car gasoline) and NH3: Soluble/Insoluble c. CH3CH2F and H2O: Soluble/Insoluble

Intermolecular Force: N/A

Intermolecular Force: Dipole-Dipole

University of Hawaii at Manoa

Chemistry 162

Professor Gary

14) How much heat is released when 23.5 grams of water vapor at 102⁰C are cooled to 5.00⁰C? (Show all work; look up specific heat values and enthalpy of fusion/vaporization in your textbook)

University of Hawaii at Manoa

Chemistry 162

Professor Gary

15) The specific heat of ethylene glycol is 2.42 J/g ⁰C. How many Joules (J) of heat are needed to raise the temperature of 62.0 grams of ethylene glycol from 15.2 ⁰C to 40.8 ⁰C? (Ethylene glycol melts at -12.9 ⁰C and boils at 197.3 ⁰C). 𝑞 = 𝑚𝐶∆𝑇 𝐽 𝑞 = (62.0 𝑔) (2.42 ) (40.8℃ − 15.2℃) = 3840 𝐽 𝑔℃ 16) In one sentence or less, explain why temperature doesn’t change during a phase change: Temperature doesn’t change during a phase change because all of the heat energy being added to the substance goes towards breaking intermolecular forces to allow the substance to go to the next highest energy phase. 17) In one sentence, explain what types of molecules (particles) have London dispersion forces: All particles have London dispersion forces, but only non-polar substances exhibit significant London dispersion forces. 18) Pick which of the following statements is most true. a. As a solution is heated the solid solutes will become more soluble b. As a solution is heated the solid solutes becomes less soluble c. As a solution is heated its boiling point is depressed d. As a solution is cooled its freezing point is elevated e. None of the above are true 19) Which of the following statements is TRUE? a. In general, the solubility of a solid in water decreases with increasing temperature. b. The solubility of a gas in water decreases with increasing temperature. c. The solubility of a gas in water usually increases with decreasing pressure. d. None of the above statements are true. 20) Which of the following concentration units is temperature dependent? a. b. c. d. e.

mole fraction molality mass percent molarity None of these

21) When a large diesel truck accelerates a black cloud of smoke is seen, this can be best describe as: a. A colloidal solution of a liquid in a gas b. A colloidal solution of a solid in a liquid c. A homogenous of two gases d. A colloidal solution of a fine particulate solid in a gas e. None of these are true

University of Hawaii at Manoa

Chemistry 162

Professor Gary

22) What is the freezing point of a 7.50 m aqueous ethylene glycol solution, C2H6O2? (KF = 1.86 °C/m) a. 14.65°C b. -7.65°C c. -13.95°C d. 140.65°C e. -1.65°C 23) Choose the solvent below that would show the greatest freezing point lowering when used to make a 0.20 m nonelectrolyte solution. a. carbon tetrachloride, Kf = 29.9°C/m b. chloroform, Kf = 4.70°C/m c. benzene, Kf = 5.12°C/m d. ethanol, Kf = 1.99°C/m e. diethyl ether, Kf = 1.79°C/m 24) Osmosis is a process that relies on a semipermeable membrane. Which best describe the membrane? a. An item that lowers the activation energy of a catalytic reaction. b. An item that allows two liquids dissolve in one another. c. A metal container that is used to experimentally calculate the heat of a reaction (enthalpy). d. A thin piece of a substance that allows only certain molecules or ions to pass through. e. None of these do. 25) Which graph best reflects the relationship of boiling point elevation with molality? (c) a)

b)

c)

d)

26) What is the mole percent of C2H6O2 in a solution prepared by mixing 17.2 g of C2H6O2 with 0.500 kg of H2O to make 515 mL of solution? 17.2 𝑔 𝐶2 𝐻6 𝑂2

𝑋

1 𝑚𝑜𝑙 𝐶2 𝐻6 𝑂2

62.08 𝑔 𝐶2 𝐻6 𝑂2

0.500 kg 𝐻2 𝑂 1000 𝑔 𝑋

1 𝑘𝑔

𝑴𝒐𝒍𝒆 % = 𝑴𝒐𝒍𝒆 % =

𝑋

= 0.2771 𝑚𝑜𝑙 𝐶2 𝐻6 𝑂2

1 𝑚𝑜𝑙 𝐻2 𝑂 = 27.75 𝑚𝑜𝑙 𝐻2 𝑂 18.02 𝑔 𝐻2 𝑂

𝑴𝒐𝒍𝒆𝒔 𝒐𝒇 𝑰𝒏𝒕𝒆𝒓𝒆𝒔𝒕 𝑻𝒐𝒕𝒂𝒍 𝑴𝒐𝒍𝒆𝒔

𝑿𝟏𝟎𝟎

0.2771 𝑚𝑜𝑙 𝐶2 𝐻6 𝑂2 𝑿𝟏𝟎𝟎 0.2771 𝑚𝑜𝑙 𝐶2 𝐻6 𝑂2 + 27.75 𝑚𝑜𝑙 𝐻2 𝑂 𝑴𝒐𝒍𝒆 % = 𝟎. 𝟗𝟖𝟗 % 𝐶2 𝐻6 𝑂2

University of Hawaii at Manoa

Chemistry 162

Professor Gary

27) How many grams of MgBr2 must be added to 1.00 kg of water to produce a solution that freezes at -5.00 ⁰C? (The following table may be useful)

∆𝑇𝑓 = 𝑖 ∗ 𝑚 ∗ 𝐾𝑓 5.00⁰C = (3)(

𝑚𝑜𝑙 𝑀𝑔𝐵𝑟2

1.00 𝑘𝑔 𝐻2 𝑂

)(1.86 ⁰C/m)

mol 𝑀𝑔𝐵𝑟2 = 0.896 mol 𝑀𝑔𝐵𝑟2 =

0.896 mol 𝑀𝑔𝐵𝑟2

𝑋

184.11 𝑔 𝑀𝑔𝐵𝑟2 1 𝑚𝑜𝑙 𝑀𝑔𝐵𝑟2

= 164 𝑔 𝑀𝑔𝐵𝑟2

28) Answer the following questions about the solubility curve below:

a. What is the solubility of potassium nitrate at 50 ⁰C? 90 g KNO3/100 g H2O b. What is the minimum amount of water would you need to fully dissolve 87 grams of sodium chloride at 90 ⁰C? 210 g H2O 40 𝑔 𝑁𝑎𝐶𝑙

100 𝑔 𝐻2 𝑂

=

87 𝑔 𝑁𝑎𝐶𝑙 𝑥 𝑔 𝐻2 0

c. At what temperature do sodium nitrate and calcium chloride have the same solubility? 23 ⁰C

University of Hawaii at Manoa

Chemistry 162

Professor Gary

29) In one sentence, explain how and why the vapor pressure of a solvent changes as solute is added. The vapor pressure of a solvent lowers as solute is added to the solvent because solute-solvent interactions are stronger than solvent-solvent interactions and decreases the amount of solvent that can escape into the gas phase causing vapor pressure. 30) The molarity of a solution of sodium phosphate, Na3PO4, in water, is 0.250 M at 24.0 ⁰C. Its density is 1.075 g/mL. For this solution, determine the following: a. Mass % of Na3PO4 solution:

b. Molality of Na3PO4 solution:

University of Hawaii at Manoa

Chemistry 162

Professor Gary

c. Mole fraction of Na3PO4 in solution:

d. Freezing point of Na3PO4 solution:

e. Boiling point of Na3PO4 solution: (Report to 2 decimal places, not correct sig figs)

f. Osmotic pressure of Na3PO4 solution:

31) True or False: The driving force of a solution to form is based on a decrease in entropy and an increase in enthalpy.

University of Hawaii at Manoa

Chemistry 162

Professor Gary

32) The concentration of stomach acid, HCl in the body is 0.100 M. If you threw up 400. mL of stomach acid, how many grams of HCl could you obtain?

33) Rank the following solutions in order of increasing boiling point: 0.500 m sucrose (C12H22O11), 0.500 m CaCl2, 0.500 m LiBr

34) Write a balanced reaction for which the following rate relationships are true. Rate = a.

N2 + O2 →

N2O

b. 2 N2O → 2 N2 + O2 c. N2O → N2 + 2 O2 d. N2O → N2 + O2 e. 2 N2 + O2 → 2 N2O

=

= -

University of Hawaii at Manoa

Chemistry 162

Professor Gary

35) Determine the rate law and the value of k for the following reaction using the data provided. CO(g) + Cl2(g) → COCl2(g) [CO]i (M) 0.25 0.25 0.50

[Cl2]i (M) 0.40 0.80 0.80

Initial Rate (M-1s-1) 0.696 1.97 3.94

a. Rate = 11 M-3/2s-1 [CO][Cl2]3/2 b. Rate = 36 M-1.8s-1 [CO][Cl2]2.8 c. Rate = 17 M-2s-1 [CO][Cl2]2 d. Rate = 4.4 M-1/2s-1 [CO][Cl2]1/2 e. Rate = 18 M-3/2s-1 [CO]2[Cl2]1/2 36) What data should be plotted to show that experimental concentration data fits a zerothorder reaction? a. ln[reactant] vs. time b. 1/[reactant] vs. time c. ln(k) vs. 1/T d. ln(k) vs. Ea e. [reactant] vs. time 37) What are the 2 key features that must be met in order for a reaction to occur? a. Enough energy and high enough temperature b. Proper orientation and the correct intermolecular force c. Enough energy and the proper catalyst d. Strong enough intermolecular forces and gaseous molecules e. None of the above (Needs proper orientation and large enough energy) 38) Consider the following reaction at 300 ⁰C: 2 NO (g) + O2 (g) → 2 NO2 (g) In the first 100.0 seconds, the concentration of O2 drops from 0.0100 M to 0.00650 M. What is the average rate of disappearance of O2 over this time interval?

University of Hawaii at Manoa

Chemistry 162

Professor Gary

39) The following kinetic data were obtained for the reaction: A (g) + B (g) → C (g) The following rate data were measured: Experiment 1 2 3 4 5

Initial Concentration of A (Molarity) 0.500 0.500 0.400 0.700 0.350

a. What is the order with respect to A?

b. What is the order with respect to B?

c. What is the overall order of the reaction?

d. Write the rate law for the reaction.

Initial Concentration of B (Molarity) 0.500 0.250 0.200 0.200 0.200

Initial Rate 𝑴 ( ) 𝒔𝒆𝒄

0.4260 0.2130 0.1364 ? 0.1192

University of Hawaii at Manoa

Chemistry 162

Professor Gary

e. Using Experiment 2, determine the value of the rate constant.

f. Use the data to predict the reaction rate for Experiment 4.

40) Consider the following oxidation of sulfur dioxide to sulfur trioxide: Step 1: 2 NO2 (g) + 2 SO2 (g) 𝑘1 2 NO (g) + 2 SO3 (g) → Step 2: 2 NO (g) + O2 (g) 𝑘2 2 NO2 (g) →

a. Answer the following questions about each elementary step: Step 1 Rate Law: Rate=k1[NO2]2[SO2]2 Step 2 Rate Law: Rate=k2[NO]2[O2]

Molecularity for Step 2: Termolecular

b. What is the overall reaction? (Make sure it’s balanced) 2 SO2 (g) + O2 (g) → 2 SO3 (g) c. What is/are the catalyst(s) in this reaction? NO2 d. What is/are the intermediate(s) in this reaction? NO e. Is this an example of homogeneous catalysis or heterogeneous catalysis?

University of Hawaii at Manoa

Chemistry 162

Professor Gary

41) Often times, medical patients receive iodine-131 for medical imaging procedures. Iodine131 decomposes through beta decay, a first-order kinetics decomposition process, and its half-life is 8.0 days. a. What is the rate constant (in

1

) for this process?

𝑑𝑎𝑦𝑠

b. If a patient was injected with 0.500 M iodine-131 solution, how many days would it take for the patient to only have 0.00500 M iodine-131 left in his/her body? (See Above) 42) The activation energy for a reaction at 700. K is 45 kJ/mol, however the rate constant for this reaction is unknown. For the same reaction at 800. K, the rate constant is 5.5x103 1 . 5 𝑀 ∗𝑠𝑒𝑐

a. What is the rate constant for the reaction at 700 K?

University of Hawaii at Manoa

Chemistry 162

Professor Gary

b. What is the overall order for this reaction?

43) On the graph provided, create an energy profile diagram given the following information for below reaction at 400 K. The activation energy for this reaction is 250.0 kJ/mol. A (g) + B (g) → C (g) + D (g) a. b. c. d. e.

ΔH = +50.0 kJ/mol

Label the reactants and products on the graph. Indicate where the activation energy is (EA) on the graph. Label the transition state. Indicate where the change in enthalpy is (ΔH) on the graph. Show how a catalyst would affect the energy profile for the reaction....