Name: Unit!!: Kinetics and Equilibrium REGENTS CHEMISTRY

Transcription

1 Name: Unit!!: Kinetics and Equilibrium REGENTS CHEMISTRY 1

2 Name: Unit!!: Kinetics and Equilibrium Collision theory states that a reaction is most likely to occur if reactant particles collide with the proper energy and orientation. (3.4d) The rate of a chemical reaction depends on several factors: temperature, concentration, nature of reactants, surface area, and the presence of a catalyst. (3.4f) Some chemical and physical changes can reach equilibrium. (3.4h) At equilibrium the rate of the forward reaction equals the rate of the reverse reaction. The measurable quantities of reactants and products remain constant at equilibrium. (3.4i) LeChatelier s principle can be used to predict the effect of stress (change in pressure, volume, concentration, and temperature) on a system at equilibrium. (3.4j) Energy released or absorbed by a chemical reaction can be represented by a potential energy diagram. (4.1c) Energy released or absorbed during a chemical reaction (heat of reaction) is equal to the difference between the potential energy of the products and the potential energy of the reactants. (4.1d) A catalyst provides an alternate reaction pathway, which has a lower activation energy than an uncatalyzed reaction. (3.4g) 2

3 Name: Unit!!: Kinetics and Equilibrium For each word, provide a short but specific definition from YOUR OWN BRAIN! No boring textbook definitions. Write something to help you remember the word. Explain the word as if you were explaining it to an elementary school student. Give an example if you can. Don t use the words given in your definition! Reaction Rate: Enthalpy: Entropy: Potential Energy: Catalyst: Activation Energy: Activated Complex: Spontaneous Reaction: LeChatelier s Principle: Concentration/Heat: Pressure/Volume: Section 1 Reaction Rates Key Ideas: Collision theory states that a reaction is most likely to occur if reactant particles collide with the proper energy and. The rate of a chemical reaction depends on several factors: temperature, concentration, nature of reactants,, and the presence of a catalyst. 3

4 More Notes: When the temperature of a reaction is the reaction rate increases and the reaction moves faster. This is a relationship. In order to make a reaction move faster, the concentration of the reactants can be. This is a relationship. When substances in the solid phase react, it is best to the surface area of the reactants. This is a relationship. When substances are gaseous, increasing the pressure of the system will the rate of reaction because particles will be closer together and collide more often. This is a relationship. Catalysts the reaction rate by providing an alternate pathway for the reaction to take place. Ionic substances react than covalent substances due to their ability to quickly dissolve and switch ions. Questions: 1. Does every reactant collision result in a product being formed? Explain your answer. 2. How can we ensure more collisions will take place in order to increase the probability of a reaction? a. b. c. d. e. 3. Refrigerated food last longer than the same food left out at room temperature. Explain. 4. In order for a reaction to occur the particles must with proper and. Therefore, the more collisions the reactant particle have, the faster the rate. 5. Matches have the potential to burn on fire. But they will not without sufficient activation energy. Explain what activation energy means and what type of activation energy the matches need. 4

5 1. Which event must always occur for a chemical reaction to take place? A) formation of a precipitate B) formation of a gas C) effective collisions between reacting particles D) addition of a catalyst to the reaction system 2. Increasing the temperature increases the rate of a reaction by A) lowering the activation energy B) increasing the activation energy C) lowering the frequency of effective collisions between reacting molecules D) increasing the frequency of effective collisions between reacting molecules 3. After being ignited in a Bunsen burner flame, a piece of magnesium ribbon burns brightly, giving off heat and light. In this situation, the Bunsen burner flame provides A) ionization energy B) activation energy C) heat of reaction D) heat of vaporization 4. As the number of effective collisions between reacting particles increases, the rate of reaction A) Decreases B) increases C) remains the same 5. In most aqueous reactions as temperature increases, the effectiveness of collisions between reacting particles A) Decreases B) increases C) remains the same 6. Given the reaction: Mg + 2 H 2 O à Mg(OH) 2 + H 2 At which temperature will the reaction occur at the greatest rate? A) 25ºC B) 50ºC C) 75ºC D) 100ºC 7. A 5.0- gram sample of zinc and a 50.- milliliter sample of hydrochloric acid are used in a chemical reaction. Which combination of these samples has the fastest reaction rate? A) a zinc strip and 1.0 M HCl(aq) B) a zinc strip and 3.0 M HCl(aq) C) zinc powder and 1.0 M HCl(aq) D) zinc powder and 3.0 M HCl(aq) 8. 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) 1.0 M HCl(aq) at 20. C B) 1.0 M HCl(aq) at 40. C C) 2.0 M HCl(aq) at 20. D) 2.0 M HCl(aq) at 40. C 9. At STP, which 4.0- gram zinc sample will react fastest with dilute hydrochloric acid? A) lump C) bar B) powdered D) sheet metal 10. Given the reaction: Fe(s) + 2 HCl(aq) à 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 less dense D) D) is more dense 11. 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 limits the amount of reactants used. C) A catalyst changes the kinds of products produced. D) A catalyst provides an alternate reaction pathway that requires less activation energy. 12. Which change would most likely increase the rate of a chemical reaction? A) decreasing a reactant's concentration B) decreasing a reactant's surface area C) cooling the reaction mixture D) adding a catalyst to the reaction mixture 5

6 Section 2 Enthalpy Review Enthalpy of the of a reaction measured by subtracting: minus. These values can be found on table. Notes: Enthalpy is a fancy word for of reaction. All exothermic reactions are given a value on Table I. Exothermic reactions are stable then endothermic reactions. Combustion reactions are the first 13 reaction on table I. What reactant do they have in common? The last 6 reactions on table I show substances dissolving. What reactant do they have in common? Questions: 1. How can you determine if a reaction is endothermic or exothermic based on the sign of ΔH? 2. If a reaction is endothermic, is the heat a reactant or product? Explain. 3. Is the formation of aluminum oxide endothermic or exothermic? 4. Is the decomposition of nitrogen dioxide endothermic or exothermic? 5. Which is more stable: C 2 H 6 or C 2 H 4? Explain. Fe 2 O 3 + 3CO à 2Fe + 3CO KJ 6. How much heat is produced when 3.56 moles of CO are used? 7. How many moles of Fe are produced when 356KJ of heat are made? 8. How much heat is produced when 56.8grams of Fe 2 O 3 are used? 6

7 1. Which compound was the most stable when synthesized on Table I? 2. Which reaction on table I requires the most heat to react? 3. How much heat is required to produce 1 mole of C 2 H 2? 4. How much heat is required to produce 2 moles of C 2 H 2? 5. If you reverse a reaction what happens to the magnitude of H? What happens to the sign? 6. If the H for a given forward reaction is positive, will the reverse reaction be endothermic or exothermic? Reaction H (kj) Endothermic and Exothermic CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(l) 2H 2 (g) + O 2 (g) 2H 2 O(g) C 2 H 5 OH(l) + 3O 2 (g) 2CO 2 (g) + 3H 2 O(l) C 3 H 8 (g) + 5O 2 (g) 3CO 2 (g) + 4H 2 O(l) 4H 2 O(l) + 3CO 2 (g) C 3 H 8 (g) + 5O 2 (g) N 2 (g) + 3H 2 (g) 2NH 3 (g) CO 2 (g) C(s) + O 2 (g) NH 4 Cl(s) NH + 4 (aq) + Cl - (aq) 2CO 2 (g) + 4H 2 O(l) 2CH 3 OH(l) + 3O 2 (g) 2Al 2 O 3 (s) 4Al(s) + 3O 2 (g) *CO(g) + ½O 2 (g) CO 2 (g) *4NO(g) 2N 2 (g) + 2O 2 (g) Methane (CH 4 ) combining with oxygen to produce carbon dioxide and water Potassium nitrate dissociating into a positive potassium ion and a negative nitrate ion Sodium hydroxide dissociating into a positive sodium ion and a negative hydroxide ion Carbon monoxide combining with oxygen to form carbon dioxide **A positive lithium ion combining with a negative bromine ion to form lithium bromide Endo or Exo Endo or Exo Endo or Exo Endo or Exo Endo or Exo 7

8 1. Given the equation representing a reaction: CH 4 (g) + 2O 2 (g) à 2H 2 O(g) + CO 2 (g) + heat Which statement is true about energy? A) The reaction is exothermic because it releases heat. B) The reaction is exothermic because it absorbs heat. C) The reaction is endothermic because it releases heat. D) The reaction is endothermic because it absorbs heat. 2. Which balanced equation represents an endothermic reaction? A) C(s) + O 2 (g) à CO 2 (g) B) CH 4 (g) + 2O 2 (g) à CO 2 (g) + 2H 2 O( ) C) N 2 (g) + 3H 2 (g) à 2NH 3 (g) D) N 2 (g) + O 2 (g)à 2NO(g) 3. Given the balanced equation representing a reaction at kpa and 298 K: N 2 (g) + 3H 2 (g) à 2NH 3 (g) kj Which statement is true about this reaction? A) It is exothermic and H equals 91.8 kj. B) It is exothermic and H equals kj. C) It is endothermic and H equals 91.8 kj. D) It is endothermic and H equals kj. 4. Which expression represents the H for a chemical reaction in terms of the potential energy, PE, of its products and reactants? A) PE of products + PE of reactants B) PE of products PE of reactants C) PE of products PE of reactants D) PE of products / PE of reactants 5. Given the balanced equation: 4Fe(s) + 3O 2 (g) à 2Fe 2 O 3 (s) kj Which phrase best describes this reaction? A) endothermic with H = kj B) endothermic with H = 1640 kj C) exothermic with H = kj D) exothermic with H = 1640 kj 6. According to Table I, which salt releases energy as it dissolves? A) KNO 3 B) LiBr C) NH 4 NO 3 D) NaCl 7. In a chemical reaction, the difference between the potential energy of the products and the potential energy of the reactants is called A) activation energy B) kinetic energy C) activated complex D) heat of reaction Key Ideas: Section 3 Potential Energy Diagram Energy released or absorbed by a chemical reaction can be represented by a diagram. Energy released or absorbed during a chemical reaction (heat of reaction) is equal to the difference between the potential energy of the and the potential energy of the. A catalyst provides an alternate reaction pathway, which has a activation energy than an uncatalyzed reaction. 8

9 More Notes: The energy is the energy needed to start a reaction. It is labeled on the diagram with. The activated complex is the point with the energy on the graph. It is labeled on the diagram with. The are always at the beginning of a reaction and is labeled here with a. The are always at the end of a reaction and is labeled here with a. The enthalpy of the reaction (or heat) is the between the products and the reactants and is labeled here with a. Reactions that have products with higher energy than reactants, such as the one in the diagram, are thermic reactions. 1. How much energy do the reactants have? Questions: 2. How much energy do the products have? 3. Is the reaction endothermic or exothermic? 4. What is the enthalpy value? 5. How much energy does the activated complex have? 6. How much energy does this reaction need to start (activation energy)? 7. If this reaction was reversed, how much activation energy would it need? 8. If this reaction was reversed, would it be 9

10 1. Define potential energy (PE). 2. Using the first diagram to the right, record the letter that describes each statement: a. Reactants PE: b. Products PE: c. Activated complex PE: d. Activation Energy: e. Heat of Reaction: 3. Is the diagram above depicting an endothermic or exothermic reaction? Defend your answer. 4. On the second diagram to the right find the value of the following statements in kj: a. Reactants PE: b. Products PE: c. Activated complex PE: d. Heat of Reaction: e. Activation Energy of the reverse reaction: f. Enthalpy of reverse reaction: 5. Is the diagram above depicting an endothermic or exothermic reaction? Defend your answer. 6. On the third diagram to the right find the value of the following statements in kj for the uncatalyzed reaction: a. Reactants PE: b. Products PE: c. Activation Energy: d. Heat of Reaction: e. Activation Energy of the reverse reaction: f. Enthalpy of reverse reaction: 7. Is the diagram above depicting an endothermic or exothermic reaction? Defend your answer. 10

11 8. On the third diagram, what values changed for the catalyzed reactions? Give the new values: a. Reactants PE: b. Activated complex PE: c. Activation Energy: d. Heat of Reaction: 9. For the reaction on table I that creates Aluminum oxide, sketch the following: 10. Using the reactions on table I, sketch a graph for the reaction that produces nitrogen monoxide: 11

12 Using the graph below please draw a reaction potential energy diagram for a reaction with the following characteristics: Potential Energy of Reactants = 350 kj/mole Activation Energy of Forward Reaction = 100 kj/mole Potential Energy of Products = 150 kj/mole Potential Energy (kj) 1. Is the reaction endothermic or exothermic? Reaction Coordinate (X + Y Z) 2. Please identify the following on the diagram you created in question #1. Place this letter above its corresponding line segment on the graph and the value in the adjacent column. Component of Potential Energy Diagram Symbol Value Potential Energy of Reactants Potential Energy of Products Potential Energy of Activated Complex Heat of Reaction Activation Energy of Forward Reaction Activation Energy of Reverse Reaction A B C D E F 3. Using a dotted line, show how the reaction potential energy diagram would be altered upon the addition of a catalyst to the reaction in the graph above. 4. If a catalyst were added, which lettered quantities, if any would change? 12

13 Section 4 Equilibrium and Entropy Key Ideas: Some chemical and physical changes can reach equilibrium. At equilibrium the rate of the forward reaction the rate of the reverse reaction. The measurable quantities of reactants and products remain constant at equilibrium. Notes: Equilibrium states that a reversible reaction has equal not necessarily equal amounts. Equilibrium requires the rate that the reaction forms products must be the rate that the reaction forms reactants. Entropy measures the in a system. The phase has the most entropy because its particles move the most. The more particles a system has, the entropy it has. This is a direct relationship. In order for a reaction to be spontaneous it should have entropy and be thermic which has a (positive or negative) value. Questions: 1. Label where equilibrium is achieved in the system. 2. Write an equation for the system at equilibrium. Entropy is the degree of in a substance. The symbol for change in entropy is S. Solids are very ordered and have low entropy. Liquids and aqueous ions have entropy than solids because they move about more freely. Gases have an even larger amount of entropy because their particles are spread out and are extremely free to move about. Nature always proceeds to a state of higher entropy (or randomness). 13

14 Determine whether the following reactions show an increase or decrease in entropy based on the individual states (s), (l), (aq), (g) within the reaction. 1) 2KClO 3(s) à 2KCl (s) + 3O 2(g) 2) H 2 O (l) à H 2 O (s) 3) N 2(g) + 3H 2(g) à 2NH 3(g) 4) NaCl (s) à Na + (aq) + Cl - (aq) 5) KCl (s) à KCl (l) 6) C (s) + O 2(g) à CO 2(g) 7) H 2(g) + Cl 2(g) à 2HCl (g) 8) Ag + (aq) + Cl - (aq) à AgCl (s) 9) 2NO (g) à N 2(g) + O 2(g) 10) H 2 O (g) à H 2 O (l) Reaction CO 2 (s) à CO 2 (g) Enthalpy (endo/exo) Entropy (Increases or decreases) Favorable or not? I 2 (g) à I 2 (s) C(s) + O 2 (g) à CO 2 (g) 4Al(s) + 2O 2 (g)à 2 Al 2 O 3 (s) 2CO(g) + O 2 (g) à 2CO 2 (g) 2H 2 (g) + O 2 (g) à 2H 2 O(l) Reaction Spontaneous or not? How did you know? 4Al(s) + 2O 2 (g)à 2 Al 2 O 3 (s) +3351kJ 2CO(g) + O 2 (g) à 2CO 2 (g) +566kJ NaOH(s) à Na + (aq) + Cl - (aq) kJ 2C(s) + 2H 2 (g) kJ à C 2 H 4 (g) Enthalpy: Entropy: Enthalpy: Entropy: Enthalpy: Entropy: Enthalpy: Entropy: 14

15 Questions: 1. Which substance has the highest entropy? a. Xe (g) b. S (s) c. Hg (s) 2. Which substance has the lowest entropy? a. H 2 O at C b. H 2 O at 0 C c. H 2 O at 100 C 3. When a system becomes less random the entropy a. Increases b. decreases c. remains the same 4. Which shows an increase in entropy? a. H 2 O (s) à H 2 O (l) b. H 2 O (g) à H 2 O (l) c. H 2 O (l) à H 2 O (s) 5. The following reactions shows the entropy is CaCO 3(s) à CaO (s) and CO 2(g) a. Increases b. decreases c. remains the same 6. The following reactions shows the entropy is 2AB à 2A+B 2 a. Increases b. decreases c. remains the same 7. A chemical reaction is spontaneous if a. There is a gain of energy and entropy increases b. There is a gain of energy and entropy decreases c. There is a loss of energy and entropy increases d. There is a loss of energy and entropy decreases If a reaction is endothermic but still spontaneous the entropy must 15

16 Section 5 LeChatelier s Principle Key Ideas: At equilibrium the rate of the forward reaction the rate of the reverse reaction. The measurable quantities of reactants and products remain constant at equilibrium. LeChatelier s principle can be used to predict the effect of (change in pressure, volume, concentration, and temperature) on a system at equilibrium. Notes: Equilibrium states that a reversible reaction has equal not necessarily equal amounts. Equilibrium requires the rate that the reaction forms products must be the rate that the reaction forms reactants. When a reactant is added the reaction shifts away from the reactant to make more. When a product is added the reaction shifts away from the product to make more. When a reactant is taken the reaction shifts from the reactant to restore it. When a product is taken the reaction shifts from the product to restore it. When heat is added to a reaction the reaction shifts from the heat, much like a reactant or product. Therefore if heat is removed (or taken) the reaction shifts heat. When a gaseous system increases in pressure or decreases in volume the system can hold fewer moles. Therefore the reaction shifts towards the side with moles. 16

17 Rules: 1. If a substance (or heat) is ADDED shift AWAY from that substance (or heat) 2. If a substance (or heat) is TAKEN shift TOWARDS that substance (or heat) 3. If pressure is added, there is less volume/room for moles. Shift towards side with less moles. 4. If pressure is relieved, there is more room. Shift towards the side with more moles. 5. Catalysts speed up the forward AND reverse reaction. Therefore equilibrium is unchanged. 6. At equilibrium RATES are equal. Not amount! 1. Circle which direction the equilibrium will shift towards to relieve the stress and cite the rule used: N 2(g) + 3H 2(g) + heat 2NH 3(g) Rule # a. Ammonia is added left right no b. Nitrogen is added left right no c. Hydrogen is added left right no d. Heat is added left right no e. Ammonia is removed left right no f. Nitrogen is removed left right no g. Hydrogen is removed left right no h. Heat is removed left right no i. Pressure is increased left right no j. Pressure is decreased left right no k. A catalyst is added left right no 17

18 2. Circle what will happen to the Nitrogen to relieve the stress: N 2(g) + 3H 2(g) + heat 2NH 3(g) a. Ammonia is removed increase decrease remain the same b. Heat is added increase decrease remain the same c. Pressure is increased increase decrease remain the same d. Heat is removed increase decrease remain the same e. Ammonia is added increase decrease remain the same f. Hydrogen is removed increase decrease remain the same g. A catalyst is used increase decrease remain the same h. Pressure is decreased increase decrease remain the same i. Hydrogen is added increase decrease remain the same 3. In a closed soda bottle the following equilibrium exists: H 3 O + (aq) + HCO 3 - (aq) 2H 2 O (l) + CO 2(g) a. When the cap is opened, the pressure decreases. Which way does the reaction shift? b. Will opening the cap result in more or less carbon dioxide dissolved in the soda? c. When the soda is left out on a hot day, which way does the equilibrium reaction shift? d. Will heating the soda result in less or more carbon dioxide dissolved in the soda? e. Why do soda companies recommend storing soda at cool temperatures with the cap on tight? 4. List four changes you could make to the system in order to produce more phosphorous pentachloride: Cl 2(g) + PCl 3(g) PCl 5(g) 18

19 5. Consider the following: N 2 O 4(g) 2NO 2(g) Colorless Brown NO 2 is placed in a flask at a constant temperature. Which of the following is true as the system approaches equilibrium? a. The color gets darker as [NO 2 ] increases. b. The color gets lighter as [NO 2 ] decreases. c. The color gets darker as [N 2 O 4 ] increases. d. The color gets lighter as [N 2 O 4 ] decreases. 6. Indicate how each of the following changes affects the amount of each gas in the system below, for which ΔH reaction = +9.9 kcal. H 2 (g) + CO 2 (g) H 2 O(g) + CO(g) a) addition of CO 2 b) addition of H 2 O c) addition of a catalyst d) increase in temperature e) decrease in the volume of the container 7. How will the amount of chemicals at equilibrium be affected by each of the following: 2N 2 O(g) + O 2 (g) 4NO(g) a) adding N 2 O b) removing O 2 c) increasing the volume of the container d) adding a catalyst 8. Match the change to the equilibrium system below with the letter of the appropriate response. Each letter can be used once, more than once, or not at all. 2SO 2(g) + O 2(g) D 2SO 3(g) 1) O 2 is added to the reaction a) The equilibrium shifts to the right 2) SO 3 is removed from the reaction b) The equilibrium shifts to the left 3) SO 3 is added to the reaction c) there is no change in the equilibrium 4) The pressure is increased 19

20 Reactions Rates and Collision Theory Reaction rates depend on effective collisions. The more collisions, the higher the probability that a reaction will take place. a. Describe how changes to each of the following will increase the rate of a reaction: Temperature: Concentration of a solution: Surface area of a solid: Pressure of a gas: Addition of a catalyst: b. In order for a reaction to take place, effective collisions are necessary. What are effective collisions? Potential Energy Diagrams PE diagrams show the heat that a reaction has, gains, or loses, throughout the mechanism. a. Label the following graph with the PE of the reactants, PE of the products, PE of the activated complex, activation energy of the forward reaction, activation energy of the reverse reaction, heat of reactions, and endothermic or exothermic. b. Which of those values are changed when a catalyst is added? c. How is the heat of reaction calculated? 20

21 Enthalpy and Entropy Enthalpy is the amount of heat lost or gained in a reaction. Entropy is the amount of disorder in a reaction. a. Determine the enthalpy of the reaction that forms CO 2 from its elements. b. What is the enthalpy of the reverse reaction on the question above? c. What is the enthalpy of double the reaction in question a? d. Which phase has the most entropy? e. How does temperature affect entropy? f. Name one phase change that would reduce the entropy of a system. LeChatelier s Principle Reactions can be stressed by the addition of reactants, products, pressure or temperature. The reaction shifts away from a substance when that substance is added and toward that substance when it is taken. Increases in pressure increases the side with less moles due to less room kcal + H 2(g) + I 2(g) D 2HI (g) Stress Equilibrium Shift [H 2 ] [I 2 ] [HI] 1. Add H 2 2. Add I 2 3. Add HI 4. Remove H 2 5. Remove I 2 6. Remove HI 7. Increase temperature 8. Decrease temperature 9. Increase pressure 10. Decrease pressure The binding of oxygen to hemoglobin (abbreviated Hb), giving oxyhemoglobin (HbO2) is partially regulated by the concentration of H+ and CO2 in the blood. Although the equilibrium is rather complicated it can be summarized as follows: HbO 2 + H + + CO 2 CO 2 HbH + + O 2 According to Le Chatelier s principle, what would be the effect of each of the following on the equilibrium: a. The production of lactic acid (contains H+) and CO2 in a muscle during exercise? b. Inhaling fresh oxygen enriched air? 21