Reaction Kinetics Multiple Choice January 1999 1. Consider the reaction: Ca (s) + 2H 2 O (l) Ca(OH) 2 (aq) + H 2 (g) At a certain temperature, 2.50 g Ca reacts completely in 30.0 seconds. The rate of consumption of Ca is A. 0.00208 mol/min B. 0.0833 mol/min C. 0.125 mol/min D. 5.00 mol/min 2. The minimum amount of energy required to overcome the energy barrier in a chemical reaction is the A. heat of reaction. B. activation energy. C. KE of the reactants. D. enthalpy of the products. 3. An activated complex is a chemical species that is A. stable and has low PE. B. stable and has high PE. C. unstable and has low PE. D. unstable and has high PE. 4. A certain reaction is able to proceed by various mechanisms. Each mechanism has a different E a and results in a different overall rate. Which of the following best describes the relationship between the E a values and the rates?
5. Consider the following PE diagram: The forward reaction can be described as 6. Consider the following reaction mechanism: In this reaction, H2 is a A. product. B. catalyst. C. reactant. D. reaction intermediate. April 1999 1. The slowest of the following reactions is A. Ag + (aq) + Cl - (aq) AgCl (s) B. H 3 O + (aq) + OH - (aq) 2H 2 O (l) C. 3Ba 2+ (aq) + 2PO 4 3- (aq) Ba 3 (PO 4 ) 2 (s) D. Cu (s) + 2Ag + (aq) Cu 2+ (aq) + 2Ag (s)
2. The rate of a chemical reaction is equal to the slope of a graph with the axes labeled 3. Consider the following reaction: CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O (g) + heat The diagram which represents the relationship between rate and temperature is: 4. Which of the following describes the energy of colliding particles as reacting molecules approach each other? 5. The average kinetic energy of colliding particles can be increased by A. adding a catalyst. B. increasing pressure. C. increasing temperature. D. increasing reactant concentration.
6. A substance that increases the rate of a chemical reaction and may be recovered unchanged at the end of the reaction is a(n) A. product. B. catalyst. C. activated complex. D. reaction intermediate. 7. Consider the following PE diagram for a reversible reaction: June 1999 1. Which of the following can be used to represent the rate of a reaction?
2. Consider the following reaction: 2H 2 O 2 (l) 2H 2 O (l) + O 2 (g) Which graph shows the relationship between rate of consumption of H2O2 and time? 3. Consider the following reaction: Mg (s) + 2HCl (aq) H 2(g) + MgCl 2(aq) The rate of this reaction increases when more magnesium is added. This change is caused by the A. addition of a catalyst. B. increase in surface area. C. change in nature of the reactants. D. increase in concentration of reactants. 4. Consider the following PE diagram:
5. Which graph shows the relationship between activation energy (E a ) and temperature? 6. A catalyst changes the rate of a reaction by A. changing H. B. increasing the temperature. C. decreasing the energy of the products. D. providing an alternate reaction mechanism. August 1999 1. At room temperature, which of the following reactions is fastest? A. 2H 2(g) + O 2 (g) 2H 2 O (g) B. Pb 2+ (aq) + 2I - (aq) PbI 2(s) C. 4Fe (s) + 3O 2(g) 2Fe 2 O 3(s) D. Cu (s) + 2Ag + (aq) Cu 2+ (aq) + 2Ag (s) 2. Consider the following reaction: CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O (g) At a certain temperature, 1.0 mol CH 4 is consumed in 4.0 minutes. The rate of production of H 2 O is A. 0.25 mol/min B. 0.50 mol/min C. 2.0 mol/min D. 8.0 mol/min 3. Consider the following reaction in a closed system: H 2(g) + I 2(g) 2HI (g) Which of the following will cause the rate of the forward reaction to decrease? A. H2 is added. B. A catalyst is added. C. The volume is increased. D. The temperature is increased.
4. The changes in PE and KE, as reactant molecules approach each other, can be represented by 5. Consider the following PE diagram: Which of the following describes this reaction? 6. A chemical reaction that gives off energy is A. exothermic and H is positive. B. exothermic and H is negative. C. endothermic and H is positive. D. endothermic and H is negative.
January 2000 1. Which of the following is most likely to have the greatest reaction rate at room temperature? A. 2H 2(g) + O 2(g) 2H 2 O (l) B. 2Ag + (aq) + CrO 4 2- (aq) Ag 2 CrO 4(s) C. Pb (s) + 2HCl (aq) PbCl 2(aq) + H 2(g) D. CH 4 (g) + 2O 2(g) CO 2(g) + 2H 2 O (g) 2. Consider the following reaction involving 1 0. g of powdered zinc: Zn (s) + 2HCl (aq) ZnCl 2 (aq) + H 2 (g) The rates, in order of fastest to slowest, are A. 1, 2, 3 B. 2, 1, 3 C. 3, 1, 2 D. 3, 2, 1 3. Activation energy can be described as the A. energy of motion. B. energy of the activated complex. C. energy difference between the reactants and the products. D. energy difference between the reactants and the activated complex. 4. Consider the following potential energy diagram for a reversible reaction: Which of the following describes the system above?
5. Increasing the temperature of a reaction increases the reaction rate by I. increasing frequency of collisions II. increasing the kinetic energy of collision III. decreasing the potential energy of collision A. I only. B. I and II only. C. II and III only. D. I, II and III. 6. What effect does a catalyst have on a reaction? A. It changes the H of a reaction. B. It increases the kinetic energy of the reactants. C. It decreases the potential energy of the products. D. It provides a reaction mechanism with a lower activation energy. April 2000 1. At 25 C, which of the following reactions is fastest? A. H 2(g) + I 2(g) 2HI (g) B. Ag + (aq) + I - (aq) AgI (s) C. C 6 H 12 O 6 (s) + 6O 2(g) 6CO 2(g) + 6H 2 O (g) D. 5C 2 O 4 2- (aq) + 2MnO 4 - (aq) + 16H + (aq) 16CO 2 (g) + 2Mn 2+ (aq) + 8H 2 O (l)
2. Consider the graph for the following reaction: CaCO 3(s) + 2HCl (aq) CaCl 2(aq) + CO 2 (g) + H 2 O (l) The average rate of reaction is greatest in the time interval A. 0-1 minute. B. 0-2 minutes. C. 0-3 minutes. D. 0-4 minutes. 3. Which of the following changes will increase the average kinetic energy of reactant molecules? A. adding a catalyst B. increasing the temperature C. increasing the surface area D. increasing the concentration 4. Consider the following potential energy diagram: Which of the following represents the heat of reaction, H, for the forward reaction? A. I B. II C. III D. IV
5. When a catalyst is added to a reaction I. the heat of reaction increases II. a new mechanism is provided III. the equilibrium constant increases A. II only B. I and II only C. II and III only D. I, II and III 6. Consider the following mechanism for a reaction: Step 1. HBr + O 2 HOOBr Step 2. HBr + HOOBr 2HOBr Step 3. 2HBr + 2HOBr 2H 2 O + 2Br 2 Which of the following statements is correct? A. Br 2 is a reactant. B. HBr is a product. C. HOBr is a catalyst. D. HOOBr is a reaction intermediate. June 2000 1. Which of the following reactions will be slowest at 25 C? A. Cu (s) + S (s) CuS (s) B. H + (aq) + OH - (aq) H 2 O (l) C. Pb 2+ (aq) + 2Cl - (aq) PbCl 2(s) D. 2NaOCl (aq) 2NaCl (aq) + O 2(g) 2. Which of the following could be used as the units for rate of a reaction? I. ml/s II. g/min III. M/min A. I only. B. I and II only. C. II and III only. D. I, II and III.
3. Consider the following reaction: Zn (s) + 2HCl (aq) ZnCl 2(aq) + H 2(g) A graph of concentration of HCl vs time could be represented by 4. Consider the following experiments, each involving equal masses of zinc and 10.0 ml of acid: The rate of reaction in order from fastest to slowest is A. I > II > III B. II > I > III C. III > I > II D. III > II > I 5. What happens to the energy of reactant molecules as they approach one another?
6. Consider the following reaction mechanism: Step 1. ClO - + H 2 O HClO + OH - Step 2. I - + HClO HIO + Cl - Step 3. HIO + OH - IO - + H 2 O The catalyst is A. IO - B. H 2 O C. ClO - D. ClOH August 2000 1. Consider the following reaction: N 2 (g) + 3H 2 (g) 2NH 3 (g) If the rate of formation of NH 3 is 4.0 x 10-4 mol/s, then the rate of consumption of H 2 is A. 2.0 X 10-4 mol/s B. 4.0 X 10 4 mol/s C. 6.0 X 10 4 mol/s D. 1.2 X 10 3 mol/s 2. Consider the following reaction: Zn (s) + 2HCl (aq) ZnCl 2 (aq) + H 2(g) Which of the following instruments could be used to monitor the rate of the reaction in an open system? I. Balance II. Pressure gauge III. ph meter A. I and II only. B. I and III only. C. II and III only. D. I, II and III. 3. Which of the following changes occur when the temperature of a reaction is increased? I. Η of the reaction increases II. Frequency of the collisions increases III. Kinetic energy of the reactants increases A. I and II only. B. I and III only. C. II and III only. D. I, II and III.
4. Which of the following is true for an activated complex? A. stable and has low PE B. stable and has high PE C. unstable and has low PE D. unstable and has high PE 5. As you increase the temperature of a reaction, the A. rate increases and the time required for the reaction increases. B. rate increases and the time required for the reaction decreases. C. rate decreases and the time required for the reaction increases. D. rate decreases and the time required for the reaction decreases. 6. Which of the following potential energy curves represents a catalyzed endothermic reaction in the forward direction? A. I B. II C. III D. IV January 2001 1. Which of the following units could be used to express reaction rate? A. ml/s B. ml/g C. g/ml D. ml/mol 2. Consider the reaction: Zn (s) + 2HCl (aq) ZnCl 2(aq) + H 2(g) The rate of production of ZnCl 2, can be increased by A. decreasing the [HCl]. B. increasing the temperature. C. increasing the volume of H 2. D. decreasing the surface area of Zn.
3. The statement, the minimum energy needed to achieve a successful collision, defines A. entropy. B. activation energy. C. the DH of reaction. D. the activated complex. 4. As an activated complex changes to products, A. potential energy changes to kinetic energy. B. kinetic energy changes to potential energy. C. kinetic energy changes to activation energy. D. potential energy changes to activation energy. 5. Consider the following PE diagram for an uncatalysed and a catalyzed reaction: Which of the following describes the forward catalyzed reaction? 6. A substance that increases the rate of a reaction without appearing in the equation for the overall reaction is a(n) A. product. B. catalyst. C. reactant. D. intermediate.
April 2001 1. Which of the following reactions occurs most rapidly at standard conditions? A. 2Fe (s) + O 2(g) 2FeO (s) B. CaO (s) + 3C (s) CaC 2(s) + CO (g) C. SnO 2(s) + 2CO (g) Sn (s) + 2CO 2(g) D. 2AgNO 3(aq) + Na 2 CrO 4(aq) Ag 2 CrO 4(s) + 2NaNO 3(aq) 2. Consider the following reaction: CaO (s) + 2HCl (aq) CaCl 2 (aq) + H 2 O (l) Which of the following could be used to measure the rate of this reaction? A. change in acidity B. change in volume C. change in pressure D. change in total mass 3. In order for a collision between reactant particles to be successful A. H must be positive. B. the system must be closed. C. there must be sufficient KE. D. the change in KE must be less than the change in PE. 4. Consider the following PE diagram: The activation energy for the forward reaction is represented by A. I B. II C. III D. IV
5. What is the relationship between the activation energy and the rate of a reaction? A. When the activation energy is high, the rate of reaction is fast. B. When the activation energy is low, the rate of reaction is slow. C. When the activation energy is high, the rate of reaction is slow. D. There is no relationship between activation energy and rate of reaction. 6. Consider the following reaction mechanism: Step 1. OCl - + H 2 O HOCl + OH - Step 2. I - + HOCl HOI + Cl - Step 3. HOI + OH - H 2 O + OH - Which of the following is correct for the overall reaction? A. HOI is a product. B. H 2 O is a reactant. C. HOCl is a catalyst. D. OH - is a reaction intermediate. June 2001 1. Which of the following reactions is slowest at room temperature? A. NH 3(g) + HCl (g) NH 4 Cl (s) B. MgCl 2(s) + Ca (s) Mg (s) + CaCl 2(s) C. HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) D. Ba(NO 3 ) 2 (aq) + Na 2 SO 4(aq) BaSO 4(s) + 2NaNO 3(aq) 2. Consider the following reaction: COCl 2(g) CO (g) + Cl 2(g) Which of the following could be used to determine reaction rate in a closed system? A. a decrease in gas pressure B. an increase in gas pressure C. a decrease in the mass of the system D. an increase in the mass of the system 3. Activation energy is defined as the A. H B. average kinetic energy. C. energy of a particle s motion. D. minimum energy needed for a successful collision.
4. Which of the following reactions is endothermic? A. CH 4(g) + 2O 2(g) CO 2(g) + 2H 2 O (l) + 890.3kJ B. 2Na 2 O 2 (s) + 2H 2 O (l) 287.0 kj 4NaOH (aq) + O 2(g) C. CaO (s) + H 2 O (l) Ca(OH) 2 (aq) H= -65.2kJ D. CaO (s) + 3C (s) CaC 2(s) + CO (g) H= +464.8kJ 5. The following diagram shows reactant molecules approaching one another: What is happening to the kinetic energy and the potential energy? 6. A proposed mechanism for a reaction is: Step 1. H 3 O + + I - HI + H 2 O Step 2. H 2 O 2 + HI H 2 O + HOI Step 3. HOI + H 3 O + + I - 2H 2 O + I 2 Step 4. I 2 + I - - I 3 In the above mechanism, which of the following is true for the overall reaction? A. HI is a catalyst B. H 3 O + is a product C. H 2 O 2 is a reactant D. H 2 O is an intermediate August 2001 1. Consider the following reaction: N 2 H 4(l) + 2H 2 O 2(l) N 2(g) + 4H 2 O (l) In 5.0seconds, 0.015mol of H 2 O 2 is consumed. The rate of production of N 2 is A. 1.5 X 10-3 mol/s B. 3.0 X 10-3 mol/s C. 6.0 X10-3 mol/s D. 1.5 X10-2 mol/s 2. Consider the following reaction:
3Fe 2 O 3(s) + CO (g) 2Fe 3 O 4(s) + CO 2(g) + 46kJ Which of the following would cause the rate of the reaction to increase? A. removing the Fe 3 O 4 B. decreasing the temperature C. increasing the surface area of Fe 2 O 3 D. increasing the volume of the reaction vessel 3. Activation energy is described as A. the energy of the activated complex. B. a point on the PE diagram where KE = PE. C. the unstable high PE structural arrangement of atoms. D. the minimum PE difference between the activated complex and the reactants. 4. What happens to the activation energy and H when a catalyst is added to a reaction? 5. Consider the following potential energy diagram for a reaction: What is the value of H for this reaction? A. -120 kj B. -30 kj C. +30 kj D. +120 kj 6. A substance that is produced in one step in a reaction mechanism and consumed
in a subsequent step, without appearing in the overall reaction, is a(n) A. catalyst. B. product. C. reactant. D. intermediate. January 2002 1. Which of the following has the greatest reaction rate? A. C (s) + O 2(g) CO 2(g) B. 2H 2 O 2 (l) 2H 2 O (l) + O 2 (g) C. 2Al (s) + 3CuCl 2(aq) 2AlCl 3(aq) + 3Cu (s) D. NaCl (aq) + AgNO 3(aq) AgCl (s) + NaNO 3(aq) 2. Which factor explains why potassium generally reacts faster than sodium? A. surface area B. temperature C. concentration D. nature of reactants 3. What happens to the PE and KE of the reactants particles as the activated complex is formed? PE KE. A. increases decreases B. increases increases C. decreases decreases D. decreases increases 4. Consider the following PE diagram:
What are the values of H and activation energy (Ea) for the forward reaction? 5. Consider the following reaction mechanism: Which of the following is a reactant in the overall reaction? A. Cl B. HCl C. CCl 3 D. CHCl 3 6. Consider the following PE diagram for a catalyzed and uncatalyzed reaction:
Which of the following describes the reverse reaction? April 2002 1. Which of the following could be used to describe the rate of a reaction? A. change in time change in mass B. change in mass change in volume C. change in volume change in time D. change in volume change in mass 2. Consider the following reaction: 2H 2 O 2(aq) 2H 2 O (l) + O 2(g) Which factor explains why the above reaction speeds up in the presence of MnO 2 (s)? A. temperature C. nature of reactants B. concentration D. presence of catalyst
3. What happens to the potential energy and the total energy as an activated complex changes into products? 4. Consider the following PE diagram: Which of the following describes the type of reaction and H for the reverse reaction?
5. Consider the following diagram for a catalyzed and uncatalyzed reaction: Which of the following describes the forward reaction? 6. Consider the following reaction mechanism: NO 2 + SO 2 SO 3 + NO NO + ½ O 2 NO 2 Identify the catalyst. A. O 2 B. NO C. SO 2 D. NO 2
Unit I Multiple Choice Answers Jan 99 April 99 June 99 Aug 99 1 C 1 D 1 D 1 B 2 B 2 D 2 A 2 B 3 D 3 D 3 B 3 C 4 C 4 A 4 C 4 A 5 A 5 C 5 A 5 D 6 C 6 B 6 D 6 B Jan 00 Apr 00 June 00 Aug 00 1 B 1 B 1 A 1 C 2 C 2 A 2 D 2 B 3 D 3 B 3 C 3 C 4 A 4 D 4 C 4 D 5 B 5 A 5 B 5 B 6 D 6 D 6 B 6 D Jan 01 Apr 01 June 01 Aug 01 1 A 1 D 1 B 1 A 2 B 2 A 2 B 2 C 3 B 3 C 3 D 3 D 4 A 4 B 4 D 4 C 5 A 5 C 5 B 5 B 6 B 6 D 6 C 6 D Jan 02 Apr 02 1 D 1 C 2 D 2 D 3 A 3 D 4 A 4 B 5 D 5 A 6 A 6 D