AP Chemistry Semester 1 Exam Review Topics Covered will be: Stoichiometry, Equations & Chemical Reactions, Thermodynamics, Kinetics, Equilibrium, Measurement including units & error AP Chemistry Semester Exam review 1. Calculate the molar solubility of barium sulfate, BaSO4, in 0.020 M sodium sulfate, Na2SO4. Ksp for BaSO4 is 1.08 x 10-10 A. 1.04 x 10-5 B. 5.4 x 10-5 C. 7.87 x 10-8 D. 5.4 x 10-9 2. Determine the standard enthalpy of reaction for the combustion of hydrogen sulfide gas, which proceeds according to the reaction shown: 2H2S(g) + 3O2(g) → 2H2O(l) + 2SO2(g) The standard enthalpies for the constituents are as follows: Formula ΔH°f (kJ mol-1) A. 3. H2S(g) -20 H2O(l) -285.8 SO2(g) -296.8 -575 kJ For the reaction Experiment A. B. C. D. B. -726 kJ 2A + C. -963 kJ B → D. -1125 kJ C , experimental data was collected for 3 trials: [A] M [B] M Initial rate M s-1 1 0.40 0.20 5.5 x 10-3 2 0.80 0.20 5.5 x 10-3 3 0.40 0.40 2.2 x 10-2 Rate = k[A][B] Rate = k[A]0[B]2 Rate = k[A]2[B]2 Rate = k[A]2[B]0 4. 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) In the above reaction, 3.10 g of NH3 reacts with 2.50 g of O2. What is the theoretical yield of NO? A. 1.88 g B. 5.46 g C. 8.20 g D. 24.0 g 5. H2O(g) + Cl2O(g) ↔ 2HOCl(g) The reaction above is allowed to come to equilibrium at room temperature. At equilibrium, the partial pressure of H 2O is 296 mm Hg, Cl2O is 15 mm Hg, and HOCl is 20 mm Hg. What is the value of K p at this temperature? A. 222 B. 11 C. 0.017 D. 0.090 6. Which of the following reactions involves the largest increase in entropy? A. AgNO3(aq) + HCl(aq) → AgCl(s) + HNO3(aq) B. N2(g) + O2(g) → C. 2NO(g) + O2(g) D. 2KClO3(s) → 2NO(g) → 2NO2(g) 2KCl(s) + 3O2(g) 7. You are supposed to prepare 250 ml of a 0.1 M solution of Pb(NO3)2 solution (molar mass = 331.2 g). You would need to mix ____ of Pb(NO3)2 with enough water to make 250 ml of solution. A. 331.2 g B. 33.12 g C. 8.28 g D. 3.312 g 8. Step 1: NO(g) + Cl2(g) ↔ NOCl2(g) fast Step 2: NO(g) + NOCl2(g) → 2NOCl(g) slow Which of the following rate laws is consistent with the reaction mechanism shown above? A. Rate = k[NO][Cl2] B. Rate = k[NO]2 C. Rate = k[NO][NOCl2] D. Rate = k[NO]2[Cl2] 9. __C6H5OH + __O2 → __CO2 + __H2O When the equation above is balanced, how many water molecules will be produced? A. 1 B. 2 C. 3 D. 4 10. What is the percentage composition of Mg in the compound Mg3(PO4)2? A. 21.92% B. 23.57% C. 27.74% D. 32.32% 11. For the reaction A + B → C + D , ΔH° = +40 kJ and ΔS° = +50 JK -1. Therefore, the reaction under standard conditions is A. Spontaneous at temperatures less than 10 K B. Spontaneous at temperatures greater than 800 K C. Spontaneous only at temperatures between 10 K and 800 K D. Spontaneous at all temperatures 12. In which of the following systems would the number of moles of the substances present at equilibrium NOT be shifted by a change in the volume of the system at constant temperature? A. SO2(g) + O2(g) ↔ 2SO3(g) ↔ B. N2(g) + 3H2(g) C. NO2(g) + SO2(g) D. N2O4(g) ↔ 2NH3(g) ↔ SO3(g) + NO(g) 2NO2(g) 13. A 0.4647 g sample of a compound containing only carbon, hydrogen and oxygen was burned in an excess of pure oxygen to yield 0.8635 g of CO2 and 0.1767 g of H2O. What is the empirical formula of the compound? A. CHO B. C2H2O C. C3H3O2 D. C6H3O2 14. When 0.200 L of 0.015 M Pb(NO3)2 is mixed with 0.300 L of 0.050 M KI, the value of Q will be ________ and the bright yellow precipitate, PbI2, _________ . (Ksp for PbI2 is 9.8 x 10-9). A. Less than Ksp; will form B. Greater than Ksp; will form C. Less than Ksp; will not form D. Greater than Ksp; will not form 15. What effect will an increase in temperature have on the reaction below? 2SO3(g) ↔ 2SO2(g) + O2(g) ΔH° = +98.3 kJ per mole SO3 A. Shift the equilibrium to the right B. Shift the equilibrium to the left C. Will have no effect on the equilibrium 16. In the rate law, Rate = k[NO]2[O2], the reaction is ___ order for NO, and ____ order for O 2, and _____ overall order. A. B. C. D. Second; first; third Second; zero; third First; second; third First; third; first 17. How many grams of silver nitrate (AgNO3) are required to produce 44.0 g of aluminium nitrate (Al(NO 3)3)? 6AgNO3 + Al2(SO4)3 → 3Ag2SO4 + 2Al(NO3)3 A. 105.3 g B. 132.0 g C. 169.9 g D. 213.0 g 18. A 2.50 kg piece of copper metal is heated from 25°C to 225°C. How much heat, in kJ, is absorbed by the copper? The specific heat capacity of copper is 0.384 J/g°C. A. 124 kJ B. 156 kJ C. 192 kJ D. 212 kJ 19. 2HF(g) ↔ H2(g) + F2(g) Keq = 1.00 x 10-2 1.00 mol HF, 0.500 mol H2, and 0.750 mol F2 are mixed in an evacuated 5.00 L flask. In which direction will the equilibrium shift to establish equilibrium? A. the equilibrium shifts to the right B. The equilibrium shifts to the left C. The system is at equilibrium 20. The Ksp of PbSO4(s) is 1.3 x 10-8. Calculate the solubility (in mol/L) of PbSO4(s) in a 0.10 M solution of Na2SO4. A. 1.3 x 10-10 B. 4.5 x 10-6 C. 1.3 x 10-5 D. 1.3 x 10-7 21. The graph shown is consistent with what type of reaction? A. Zero order B. First order C. Second order Third order D. 22. The rate expression for a particular reaction is Rate = k[P][Q] Which of the units below is a possible unit for k? A. mol–2 dm6 min–1 B. mol–1 dm3 min–1 C. mol dm3 min–1 D. mol–2 dm–6 min–1 23. The average bond enthalpies for O—O and O==O are 146 and 496 kJ mol–1 respectively. What is the enthalpy change, in kJ, for the reaction below? H—O—O—H(g) → H—O—H(g) + ½O==O(g) A. – 102 B. + 102 C. + 350 D. + 394 24. What will happen to the volume of a fixed mass of gas when its pressure and temperature (in Kelvin) are both doubled? A. It will not change. B. It will increase. C. It will decrease. D. The change cannot be predicted. 25. Lithium hydroxide reacts with carbon dioxide as follows. 2LiOH + CO2 → Li2 CO3 + H2O What mass (in grams) of lithium hydroxide is needed to react with 11 g of carbon dioxide? A. 6 B. 12 C. 24 D. 48 26. Excess magnesium was added to a beaker of aqueous hydrochloric acid on a balance. A graph of the mass of the beaker and contents was plotted against time (line 1). What change in the experiment could give line 2? I. The same mass of magnesium but in smaller pieces II. The same volume of a more concentrated solution of hydrochloric acid III. A lower temperature A. I only B. II only C. III only D. None of the above 27. When 40 joules of heat are added to a sample of solid H2O at –16.0°C the temperature increases to –8.0°C. What is the mass of the solid H2O sample? [Specific heat capacity of H2O(s) = 2.0 J g–1K–1] A. 2.5 g B. 5.0 g C. 10 g D. 160 g 28. The percentage by mass of the elements in a compound is C = 72%, H = 12%, O = 16%. What is the mole ratio of C:H in the empirical formula of this compound? A. 1 : 1 B. 1 : 2 C. 1 : 6 D. 6 : 1 48. According to the enthalpy level diagram below, what is the sign for ΔH and what term is used to refer to the reaction? ΔH reaction A. B. C. D. positive negative positive negative endothermic exothermic exothermic endothermic Free-response 1. Write balanced symbol equations for the laboratory situations described below. In all cases, a reaction occurs. Assume that solutions are aqueous unless otherwise indicated. Example: A strip of magnesium is added to a solution of silver nitrate Mg + 2Ag+ → Mg2+ + 2Ag a. Butanol is burned in air b. Excess hydrochloric acid solution is added to a solution of potassium hydrogen carbonate c. Calcium oxide powder is added to distilled water d. Solid ammonium nitrate is heated to temperatures above 300°C e. Solid lead (II) carbonate is added to 0.5 M sulfuric acid solution f. A mixture of powdered iron (III) oxide and powdered aluminum is heated strongly g. A 0.2 M barium nitrate solution is added to an alkaline 0.2 M potassium chromate solution 2. Consider the equations represented below. a. O3(g) + NO(g) → O2(g) + NO2(g) Referring to the data in the table below, show that the standard enthalpy change, ΔH°, for the reaction at 25°C is 200 kJ. O3(g) NO(g) NO2(g) Standard enthalpy of formation, ΔH°f, at 25°C (kJ mol-1) b. c. d. 90 33 Make a qualitative prediction about the magnitude of the standard entropy change, ΔS°, for the reaction at 25°C. Justify your answer. On the basis of your answers to parts a. and b., predict the sign of the standard free-energy change, ΔG°, for the reaction at 25°C. Explain your reasoning. Use the information in the table below to write the rate-law expression for the reaction, and explain how you obtained your answer. Experiment number e. 143 Initial [O3] (mol L-1) Initial [NO] (mol L-1) Initial rate of formation of NO2 (mol L-1 s-1) 1 0.0010 0.0010 x 2 0.0010 0.0020 2x 3 0.0020 0.0010 2x 4 0.0020 0.0020 4x The following tree-step mechanism is proposed for the reaction. Identify the step that must be the slowest in order for this mechanism to be consistent with the rate-law expression derived in part d. Explain Step I: O3 + NO → O + NO3 Step II: O + O3 Step III: NO3 + → NO 2O2 → 2NO2 3. An equation for the decomposition of substance A is 2A → 2B + C A graph showing the change in concentration of A against time as the reaction proceeds at a particular temperature is shown below. a. b. Define the term half-life of reaction. Use the graph to measure values of half-life of reaction, starting from time = zero time = 1000 s c. Deduce the order of the reaction with respect to A, giving a reason for your choice, and write the rate expression for the reaction. d. For a different reaction, between compounds D and E, the rate expression is rate = k[D]2[E] Calculate the value of k, including units, for the reaction when the concentrations of both D and E are 1.35×10–2 mol dm–3 and the reaction rate is 3.75×10–5 mol dm–3 min–1. 4. A B C a. ( The diagram shows the distribution of energy for the molecules in a sample of gas at a given temperature, T1. a. In the diagram Ea represents the activation energy for a reaction. Define this term. b. On the diagram above draw another curve to show the energy distribution for the same gas at a higher temperature. Label the curve T2. c. With reference to your diagram, state and explain what happens to the rate of a reaction when the temperature is increased. 6. A certain line in the spectrum of atomic hydrogen is associated with the electron transition in the H atom from the sixth energA rate study of the reaction represented below was conducted at 25°C. The data that were obtained are shown in the table underneath. 2NO(g) + Br2(g) → 2NOBr(g) a. b. c. d. Experiment Initial [NO] (mol L-1) Initial [Br2] (mol L-1) Initial rate of formation of NO2 (mol L-1 s-1) 1 0.0160 0.0120 3.24 x 10-4 2 0.0160 0.0240 6.38 x 10-4 3 0.0320 0.0060 6.42 x 10-4 Calculate the initial rate of disappearance of Br2(g) in experiment 1 Determine the order of the reaction with respect to each reactant, Br 2(g) and NO(g). In each case, explain your reasoning. For the reaction, i. Write the rate law that is consistent with the data, and ii. Calculate the value of the specific rate constant, k, and specify units The following mechanism was proposed for the reaction: Br2(g) + NO(g) → NOBr2(g) slow NOBr2(g) + NO(g) → 2NOBr(g) fast Explain whether this mechanism is supported by the rate expression. If not, suggest an alternative. 7. Answer the following questions in terms of thermodynamics principles and concepts of kinetic molecular theory. a. Consider the reaction represented below, which is spontaneous at 298 K. CO2(g) + 2NH3(g) → CO(NH2)2(s) + H2O(l) ΔH°298 = -134 kJ i. For the reaction, indicate whether the standard entropy change, ΔS° 298, is positive, or negative, or zero. Justify your answer. ii. Which factor, the change in enthalpy, ΔH°298, or the change in entropy, ΔS°298, provides the principal driving force for the reaction at 298 K? Explain. iii. For the reaction, how is the value of the standard free energy change, ΔG°, affected by an increase in temperature? Explain. b. Some reactions that are predicted by their sign of ΔG° to be spontaneous at room temperature do not proceed at a measurable rate at room temperature. i. Account for this apparent contradiction. ii. A suitable catalyst increases the rate of such a reaction. What effect does the catalyst have on ΔG° for the reaction? Explain. 11. The graph below shows the volume of carbon dioxide gas produced against time when excess calcium carbonate is added to x cm3 of 2.0 mol dm–3 hydrochloric acid. a. b. Write a balanced equation for the reaction. State and explain the change in the rate of reaction with time. Outline how you would determine the rate of the reaction at a particular time. c. Sketch the above graph on an answer sheet. On the same graph, draw the curves you would expect if: I. the same volume (x cm3) of 1.0 mol dm–3 HCl is used. II. double the volume (2x cm3) of 1.0 mol dm–3 HCl is used. Label the curves and explain your answer in each case. 12. a. Draw a graph to show the distribution of energies in a sample of gas molecules. Label the axes and label your curve T1. Using the same axes, draw a second curve to represent the distribution of energies at a higher temperature. Label this curve T2. b. State and explain, with reference to your graph, what happens to the rate of a reaction when the temperature is increased.