Name: 7171-1 - Page 1 1) In a chemical reaction, the difference between the potential energy of the products and the potential energy of the reactants is defined as the A) heat of reaction B) ionization energy 2) Given the reaction: CH 4 (g) + 2O 2 (g) 2H 2 O(g) + CO 2 (g) C) activation energy D) heat of vaporization What is the overall result when CH 4 (g) burns according to this reaction? A) Energy is absorbed and DH is positive. B) Energy is released and DH is negative. C) Energy is released and DH is positive. D) Energy is absorbed and DH is negative. 3) Which statement correctly describes an endothermic chemical reaction? A) The products have lower potential energy than the reactants, and the DH is negative. B) The products have higher potential energy than the reactants, and the DH is negative. C) The products have lower potential energy than the reactants, and the DH is positive. D) The products have higher potential energy than the reactants, and the DH is positive. 4) Which balanced equation represents an endothermic reaction? A) N 2 (g) + O 2 (g) 2NO(g) C) N 2 (g) + 3H 2 (g) 2NH 3 (g) B) C(s) + O 2 (g) CO 2 (g) D) CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(l) 5) According to the Heats of Reaction at 101.3 kpa and 298 K chemistry reference table, which salt releases energy as it dissolves? A) KNO 3 B) NH 4 NO 3 C) LiBr D) NaCl 6) Based on the Heats of Reaction at 101.3 kpa and 298 K chemistry reference table, which change occurs when pellets of solid NaOH are added to water and stirred? A) The water temperature increases as chemical energy is converted to heat energy. B) The water temperature increases as heat energy is stored as chemical energy. C) The water temperature decreases as chemical energy is converted to heat energy. D) The water temperature decreases as heat energy is stored as chemical energy. 7) Given the reaction: 2H 2 (g) + O 2 (g) 2H 2 O(l) + 571.6 kj What is the approximate DH for the formation of 1 mole of H 2 O(l)? A) -571.6 kj B) -285.8 kj C) +285.8 kj D) +571.6 kj
7171-1 - Page 2 8) According to the Heats of Reaction at 101.3 kpa and 298 K chemistry reference table, which potential energy diagram best represents the reaction that forms H 2 O(l) from its elements? A) C) B) D) 9) Which information about a chemical reaction is provided by a potential energy diagram? A) the change in solubility of the reacting substances B) the oxidation states of the reactants and products C) the average kinetic energy of the reactants and products D) the energy released or absorbed during the reaction 10) When a spark is applied to a mixture of hydrogen and oxygen, the gases react explosively. Which potential energy diagram best represents the reaction? A) C) B) D)
11) The potential energy diagram below represents a reaction. 7171-1 - Page 3 Which arrow represents the activation energy of the forward reaction? A) A B) B C) C D) D 12) Given the potential energy diagram for a chemical reaction: Which statement correctly describes the energy changes that occur in the forward reaction? A) The activation energy is 50. kj and the reaction is exothermic. B) The activation energy is 10. kj and the reaction is exothermic. C) The activation energy is 50. kj and the reaction is endothermic. D) The activation energy is 10. kj and the reaction is endothermic. 13) Increasing the temperature increases the rate of a reaction by A) increasing the frequency of effective collisions between reacting molecules B) lowering the frequency of effective collisions between reacting molecules C) increasing the activation energy D) lowering the activation energy 14) In most aqueous reactions as temperature increases, the effectiveness of collisions between reacting particles A) decreases B) remains the same C) increases 15) A 1.0-gram piece of zinc reacts with 5 milliliters of HCl(aq). Which of these conditions of concentration and temperature would produce the greatest rate of reaction? A) 2.0 M HCl(aq) at 20.DC B) 1.0 M HCl(aq) at 40.DC C) 1.0 M HCl(aq) at 20.DC D) 2.0 M HCl(aq) at 40.DC 16) At STP, which 4.0-gram zinc sample will react fastest with dilute hydrochloric acid? A) bar B) lump C) sheet metal D) powdered
17) Which statement best explains the role of a catalyst in a chemical reaction? A) A catalyst is added as an additional reactant and is consumed but not regenerated. B) A catalyst provides an alternate reaction pathway that requires less activation energy. C) A catalyst changes the kinds of products produced. D) A catalyst limits the amount of reactants used. 18) A catalyst is added to a system at equilibrium. If the temperature remains constant, the activation energy of the forward reaction A) decreases B) increases C) remains the same 19) Which phase change represents a decrease in entropy? A) solid to liquid B) solid to gas C) gas to liquid D) liquid to gas 20) Given the balanced equation: I 2 (s) + energy I 2 (g) 7171-1 - Page 4 As a sample of I 2 (s) sublimes to I 2 (g), the entropy of the sample A) increases because the particles are more randomly arranged B) decreases because the particles are less randomly arranged C) increases because the particles are less randomly arranged D) decreases because the particles are more randomly arranged 21) At STP, a sample of which element has the highest entropy? A) Br 2 (l) B) Hg(l) C) Na(s) D) F 2 (g) 22) Which equation shows an increase in entropy? A) CH 3 OH(g) CH 3 OH(l) B) CH 3 OH(l) CH 3 OH(s) C) CO 2 (l) CO 2 (g) D) CO 2 (g) CO 2 (s) 23) Given the balanced equation: KNO 3 (s) + 34.89 kj K + (aq) + NO 3 - (aq) Which statement best describes this process? A) It is exothermic and entropy decreases. B) It is endothermic and entropy decreases. 24) Systems in nature tend to undergo changes toward A) higher energy and lower entropy B) higher energy and higher entropy C) It is exothermic and entropy increases. D) It is endothermic and entropy increases. C) lower energy and higher entropy D) lower energy and lower entropy 25) On the set of axes below, sketch the potential energy diagram for an endothermic chemical reaction that shows the activation energy and the potential energy of the reactants and the potential energy of the products.
Questions 26 and 27 refer to the following: 7171-1 - Page 5 In the smelting of iron ore, Fe 2 O 3 is reduced in a blast furnace at high temperature by a reaction with carbon monoxide. Crushed limestone, CaCO 3, is also added to the mixture to remove impurities in the ore. The carbon monoxide is formed by the oxidation of carbon (coke), as shown in the following reaction: 2C + O 2 2CO + energy Liquid iron flows from the bottom of the blast furnace and is processed into different alloys of iron. 26) Balance the equation below for the reaction of Fe 2 O 3 and CO described, using the smallest whole-number coefficients. Fe 2 O 3 + CO Fe + CO 2 27) Using the set of axes provided, sketch a potential energy diagram for the reaction of carbon and oxygen that produces the carbon monoxide in the situation described. Questions 28 and 29 refer to the following: The diagram below represents the changes in potential energy that occur during the given reaction: A + B C. 28) Does the diagram illustrate an exothermic or an endothermic reaction? [State one reason, in terms of energy, to support your answer.] 29) On the given above, draw a dashed line to indicate a potential energy curve for the reaction if a catalyst is added.
Questions 30 through 32 refer to the following: 7171-1 - Page 6 Chemical cold packs are often used to reduce swelling after an athletic injury. The diagram below represents the potential energy changes when a cold pack is activated. 30) Which lettered interval on the given diagram represents the potential energy of the products? 31) Which lettered interval on the given diagram represents the heat of reaction? 32) Identify a reactant listed in the Heats of Reaction at 101.3 kpa and 298 K chemistry reference table that could be mixed with water for use in a chemical cold pack. Questions 33 through 35 refer to the following: Given the potential energy diagram and the equation below: 2C(s) + H 2 (g) + 227.4 kj C 2 H 2 (g) 33) The letter B in the diagram represents which chemical formula or formulas in the equation? 34) Based on the given information, how many moles of C 2 H 2 (g) are produced if 682.2 kilojoules are absorbed? 35) Describe how the potential energy diagram shown will change if a catalyst is added.
36) Given the balanced equation for an organic reaction between butane and chlorine that takes place at 300.DC and 101.3 kilopascals: C 4 H 10 + Cl 2 C 4 H 9 Cl + HCl 7171-1 - Page 7 Explain, in terms of collision theory, why the rate of the reaction shown would decrease if the temperature of the reaction mixture was lowered to 200.DC with pressure remaining unchanged. 37) A student wishes to determine how the rate of reaction of magnesium strips with hydrochloric acid, HCl(aq), varies as a function of temperature of the HCl(aq). Give two additional factors, other than the temperature, that could affect the rate of reaction and must be held constant during the experiment. Questions 38 through 40 refer to the following: A student conducts an experiment to determine how the temperature of water affects the rate at which an antacid tablet dissolves in the water. The student has three antacid tablets of the same size and composition. The student drops one tablet into each of three beakers containing 200. milliliters of water at different temperatures and measures the time it takes for each tablet to completely dissolve. The results are shown in the table below. 38) According to the information given, describe the effect of water temperature on the rate of dissolving. 39) Explain, in terms of collision theory, how water temperature influences the rate of dissolving the antacid tablets described in the experiment. 40) What change, other than temperature, would affect the rate of dissolving the antacid tablet described in the experiment? Questions 41 and 42 refer to the following: Given the equation for the dissolving of sodium chloride in water: NaCl(s) Na + (aq) + Cl - (aq) 41) Describe what happens to entropy during the dissolving process shown. 42) When NaCl(s) is added to water in a 250-milliliter beaker, the temperature of the mixture is lower than the original temperature of the water. Describe this observation in terms of heat flow.
43) Which type or types of change, if any, can reach equilibrium? A) both a chemical and a physical change B) a physical change, only 44) Which statement about a system at equilibrium is true? A) The forward reaction rate is greater than the reverse reaction rate. B) The forward reaction rate is equal to the reverse reaction rate. C) The forward reaction rate is less than the reverse reaction rate. D) The forward reaction rate stops and the reverse reaction rate continues. 45) Which statement must be true about a chemical system at equilibrium? A) The rate of the forward reaction is equal to the rate of the reverse reaction. B) The forward and reverse reactions stop. C) The number of moles of reactants is equal to the number of moles of product. D) The concentration of reactants and products are equal. 46) Given the equilibrium reaction at STP: N 2 O 4 (g) Š 2NO 2 (g) C) neither a chemical nor a physical change D) a chemical change, only 7171-1 - Page 8 Which statement correctly describes this system? A) The forward and reverse reaction rates are both increasing. B) The concentrations of N 2 O 4 and NO 2 are both increasing. C) The concentrations of N 2 O 4 and NO 2 are equal. D) The forward and reverse reaction rates are equal. 47) Given the reaction: AgCl(s) Ag + (aq) + Cl - (aq) Once equilibrium is reached, which statement is accurate? A) The concentration of Ag + (aq) is greater than the concentration of Cl - (aq). B) The rates of the forward and reverse reactions are equal. C) The entropy of the forward reaction will continue to decrease. D) The AgCl(s) will be completely consumed. 48) Given the reaction at equilibrium: H 2 (g) + Br 2 (g) Š 2HBr(g) The rate of the forward reaction is A) independent of the rate of the reverse reaction C) greater than the rate of the reverse reaction B) equal to the rate of the reverse reaction D) less than the rate of the reverse reaction 49) A solution that is at equilibrium must be A) concentrated B) unsaturated C) saturated D) dilute 50) A student adds solid KCl to water in a flask. The flask is sealed with a stopper and thoroughly shaken until no more solid KCl dissolves. Some solid KCl is still visible in the flask. The solution in the flask is A) saturated and is at equilibrium with the solid KCl B) unsaturated and is at equilibrium with the solid KCl C) saturated and is not at equilibrium with the solid KCl D) unsaturated and is not at equilibrium with the solid KCl
7171-1 - Page 9 51) Given the diagram below that shows carbon dioxide in an equilibrium system at a temperature of 298 K and a pressure of 1 atm: Which changes must increase the solubility of the carbon dioxide? A) decrease pressure and increase temperature B) increase pressure and decrease temperature 52) Given the reaction at equilibrium: C) increase pressure and increase temperature D) decrease pressure and decrease temperature A(g) + B(g) Š AB(g) + heat The concentration of A(g) can be increased by A) adding a catalyst B) increasing the concentration of B(g) 53) Given the equilibrium reaction in a closed system: C) increasing the concentration of AB(g) D) lowering the temperature H 2 (g) + I 2 (g) + heat Š 2HI(g) What will be the result of an increase in temperature? A) The equilibrium will shift to the left and [H 2 ] will decrease. B) The equilibrium will shift to the right and [HI] will decrease. C) The equilibrium will shift to the right and [HI] will increase. D) The equilibrium will shift to the left and [H 2 ] will increase. 54) Given the system at equilibrium: N 2 O 4 (g) + 58.1 kj Š 2NO 2 (g) What will be the result of an increase in temperature at constant pressure? A) The equilibrium will shift to the left, and the concentration of NO 2 (g) will decrease. B) The equilibrium will shift to the left, and the concentration of NO 2 (g) will increase. C) The equilibrium will shift to the right, and the concentration of NO 2 (g) will decrease. D) The equilibrium will shift to the right, and the concentration of NO 2 (g) will increase. 55) Human blood contains dissolved carbonic acid, H 2 CO 3, in equilibrium with carbon dioxide and water. The equilibrium system is shown below. H 2 CO 3 (aq) Š CO 2 (aq) + H 2 O(l) Explain, using Le Chatelier's principle, why decreasing the concentration of CO 2 in the given equilibrium system decreases the concentration of H 2 CO 3.
56) Given the equilibrium equation at 298 K: 7171-1 - Page 10 KNO 3 (s) + 34.89 kj K + (aq) + NO 3 - (aq) Describe, in terms of Le Chatelier's principle, why an increase in temperature increases the solubility of KNO 3 in the equilibrium equation shown. 57) Given the reaction at equilibrium: 2NO 2 (g) + 7H 2 (g) Š 2NH 3 (g) + 4H 2 O(g) + 1,127 kj On the diagram below, complete the potential energy diagram for the forward reaction shown. Be sure your drawing shows the activation energy and the potential energy of the products.
Questions 58 through 60 refer to the following: 7171-1 - Page 11 In a laboratory, 0.100 mole of colorless hydrogen iodide gas at room temperature is placed in a 1.00-liter flask. The flask is sealed and warmed, causing the HI(g) to start decomposing to H 2 (g) and I 2 (g). Then the temperature of the contents of the flask is kept constant. During this reaction, the contents of the flask change to a pale purple-colored mixture of HI(g), H 2 (g), and I 2 (g). When the color of the mixture in the flask stops changing, the concentration of I 2 (g) is determined to be 0.013 mole per liter. The relationship between concentration and time for the reactant and products is shown in the graph below. 58) Write a balanced equation to represent the decomposition reaction occurring in the flask described. 59) State, in terms of concentration, evidence that indicates the system in the flask described has reached equilibrium. 60) For the experiment shown, calculate the mass of I 2 (g) in the flask at equilibrium. [Your response must include both a correct numerical setup and the calculated result.]