Name Chemistry Exam #8 Period: Unit 8: Kinetics, Thermodynamics, & Equilibrium

Transcription

1 1. Which quantities must be equal for a chemical reaction at equilibrium? (A) the potential energies of the reactants and products (B) the concentrations of the reactants and products (C) the activation energies of the forward and reverse reactions (D) the rates of the forward and reverse reactions 2. Given the potential energy diagram for a reaction: Which intervals are affected by the addition of a catalyst? (A) 1 and 2 (B) 1 and 3 (C) 2 and 4 (D) 3 and 4 3. Which diagram best represents a gas in a closed container? (A) (B) (C) (D) 4. Given the equation representing a reaction at equilibrium: N2(g) + 3H2(g) 2NH3(g) What occurs when the concentration of H2(g) is increased? (A) The equilibrium shifts to the left, and the concentration of N2(g) decreases. (B) The equilibrium shifts to the left, and the concentration of N2(g) increases. (C) The equilibrium shifts to the right, and the concentration of N2(g) decreases. (D) The equilibrium shifts to the right, and the concentration of N2(g) increases 5. Which conditions will increase the rate of a chemical reaction? (A) decreased temperature and decreased concentration of reactants (B) increased temperature and decreased concentration of reactants (C) decreased temperature and increased concentration of reactants (D) increased temperature and increased concentration of reactants 6. As the temperature of a chemical reaction in the gas phase is increased, the rate of the reaction increases because (A) the required activation energy increases (B) the concentration of the reactants increases (C) more effective particle collisions occur (D) fewer particle collisions occur 7. A solution that is at equilibrium must be (A) concentrated (B) unsaturated (C) dilute (D) saturated 8. A reaction is most likely to occur when reactant particles collide with (A) proper orientation, only (B) proper energy, only (C) neither proper energy nor proper orientation (D) both proper energy and proper orientation Page 1 Version 2

2 9. Given the potential energy diagram for a chemical reaction: 11. The potential energy diagram for a chemical reaction is shown below. 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 endothermic. (C) The activation energy is 50. kj and the reaction is endothermic. (D) The activation energy is 10. kj and the reaction is exothermic. 10. Entropy is a measure of the (A) chemical activity of an element (B) acidity of a sample (C) disorder of a system (D) concentration of a solution Each interval on the axis labeled "Potential Energy (kj)" represents 40 kilojoules. What is the heat of reaction? (A) 40kJ (B) +40kJ (C) 120kJ (D) +160kJ 12. The entropy of a sample of CO2 increases as the CO2 changes from (A) gas to liquid (B) gas to solid (C) solid to gas (D) liquid to solid Page 2 Version 2

3 13. Which potential energy diagram represents the change in potential energy that occurs when a catalyst is added to a chemical reaction? (A) (C) (B) (D) 14. Given the diagram representing a closed system at constant temperature: Which statement describes this system at equilibrium? (A) The volume of H2O( ) equals the volume of H2 O(g). (B) The number of moles of H2O( ) equals the number of moles of H2O(g). (C) The mass of H2O( ) equals the mass of H2O(g). (D) The rate of evaporation of H2O( ) equals the rate of condensation of H2O(g). 15. Given the balanced equation representing a reaction at kpa and 298 K: N2(g) + 3H2(g) 2NH3(g) kj Which statement is true about this reaction? (A) It is endothermic and H equals kj. (B) It is endothermic and H equals 91.8 kj. (C) It is exothermic and H equals kj. (D) It is exothermic and H equals 91.8 kj. 16. According to the kinetic molecular theory, the particles of an ideal gas (A) are arranged in a regular, repeated geometric pattern (B) have strong intermolecular forces (C) have no potential energy (D) are separated by great distances, compared to their size Page 3 Version 2

4 17. Given the reaction: Fe(s) + 2 HCl(aq) FeCl2(aq) + H2(g) In this reaction, 5 grams of powdered iron will react faster than a 1-gram piece of solid iron because the powdered iron (A) has less surface area (B) has more surface area (C) is more dense (D) is less dense 18. Given the reaction at equilibrium: N2(g) + 3 H2(g) «2 NH3(g) + 22 kcal 22. Given the potential energy diagram and equation representing the reaction between substances A and D: Which stress would cause the equilibrium to shift to the left? (A) adding H2(g) to the system (B) increasing the pressure (C) adding N2(g) to the system (D) increasing the temperature 19. In a chemical reaction, the difference between the potential energy of the products and the potential energy of the reactants is equal to the (A) heat of reaction (B) activation energy (A) 750 K and 600 kpa (B) 50 K and 20 kpa (C) rate of reaction (D) kinetic energy 20. Under which conditions of temperature and pressure would helium behave most like an ideal gas? (C) 750 K and 20 kpa (D) 50 K and 600 kpa 21. Adding a catalyst to a chemical reaction results in (A) a decrease in activation energy and a decrease in the reaction rate (B) an increase in activation energy and a decrease in the reaction rate (C) a decrease in activation energy and an increase in the reaction rate (D) an increase in activation energy and an increase in the reaction rate According to Table I, substance G could be (A) H2O(g) (B) CO2(g) (C) HI(g) (D) C2H6(g) 23. Given the reaction at equilibrium: 2 SO2(g) + O2(g) «2 SO3(g) + heat Which change will shift the equilibrium to the right? (A) decreasing the amount of SO2(g) (B) decreasing the amount of O2(g) (C) increasing the temperature (D) increasing the pressure Page 4 Version 2

5 Base your answers to questions 24 through 26 on the equation below. 2H2(g) + O2(g) 2H2O( ) kj 24. Identify the information in this equation that indicates the reaction is exothermic. 25. On the axes below, draw a potential energy diagram for the reaction represented by this equation. 26. Explain why the entropy of the system decreases as the reaction proceeds. Page 5 Version 2

6 27. Base your answer to the following question on the information below. At 550 C, 1.00 mole of CO2(g) and 1.00 mole of H2(g) are placed in a 1.00-liter reaction vessel. The substances react to form CO(g) and H2O(g). Changes in the concentrations of the reactants and the concentrations of the products are shown in the graph below. What can be concluded from the graph about the concentrations of the reactants and the concentrations of the products between time t 1 and time t 2? Page 6 Version 2

7 Base your answers to questions 28 and 29 on the information below. The chemical reaction between methane and oxygen is represented by the potential energy diagram and balanced equation below. 28. Which potential energy interval in the diagram represents the activation energy of the forward reaction? 29. Explain, in terms of collision theory, why a lower concentration of oxygen gas decreases the rate of this reaction. 30. Base your answer to the following question on the information below. Several steps are involved in the industrial production of sulfuric acid. One step involves the oxidation of sulfur dioxide gas to form sulfur trioxide gas. A catalyst is used to increase the rate of production of sulfur trioxide gas. In a rigid cylinder with a movable piston, this reaction reaches equilibrium, as represented by the equation below. State, in terms of the concentration of SO3(g), what occurs when more O2(g) is added to the reaction at equilibrium. Page 7 Version 2

8 Answer Key Exam 8 : Kinetics D 2. B 3. C 4. C 5. D 6. C 7. D 8. D 9. D 10. C 11. B 12. C 13. D 14. D 15. D 16. D 17. B 18. D 19. A 20. C 21. C 22. C 23. D 24. Examples: Heat term is on the right side of the equation. The 571.6kJ is a product Examples: A liquid is formed from gases. A compound is formed from its elements. The number of gas particles in the system decreases. 27. Between time t 1 and time t 2, the concentrations of the reactants and the concentrations of the products are no longer changing. The concentrations of the reactants and the products remain constant. The concentration of each reactant is 0.73 mol/l, and the concentration of each product is 0.27 mol/l. 28. B 29. Acceptable responses include, but are not limited to: A lower concentration of oxygen gas decreases the number of effective collisions between O2 molecules and CH4 molecules. 30. The concentration of SO3(g) increases. Page 8 Version 2