Kinetics & Equilibrium

Transcription

1 Kinetics & Equilibrium Name: Essential Questions How can one explain the structure, properties, and interactions of matter? Learning Objectives Explain Collision Theory Molecules must collide in order to react, and the must collide with the correct or appropriate orientation and with sufficient energy to equal or exceeded the activation energy. Explain qualitatively that reaction rate is proportional to number of effective collisions Explain the nature of reactants can refer to their complexity and the number of bonds that must be broken and reformed in the course of the reaction Explain how temperature (kinetic energy), concentration, and/or pressure affects the number of collisions Explain how increased surface area increases the number of collisions Explain how a catalyst lowers the activation energy, so that at a given temperature, more molecules will have energy equal to or greater than the activation energy Interpret potential energy diagrams for endothermic and exothermic reactions including reactants, products, and activated complex with and without the presence of a catalyst. Define chemical equilibrium for reversible reactions Distinguish between equal rates and equal concentrations Explain equilibrium expressions for a given reaction Evaluate equilibrium constants as a measure of the extent that the reaction proceeds to completion Determine the effects of stresses on systems at equilibrium (Adding/removing a reactant or product; adding/removing heat; increasing/decreasing pressure) Packet Contents Notes 2 13 Multiple Choice Practice (2 per page) Packet Does NOT Include: In-Class Demonstrations In-Class Activities Page 1 B. Mack

2 Collision Theory and Rates of Reaction Name: Date: Period: Kinetics = study of the Part A: Speed of reactions Not all reactions happen at the same rate. Fast Explosions Slow Rust Rate of a Reaction: Part B: Collision Theory: What would cause a reaction to occur? For a reaction to occur: READ ME: We know that positives and negatives go together, and that CaCl 2 will be a product, so the Cl and Ca must collide, or no reaction will occur. Not only that, but they must collide with enough energy, just like if two cars collide they won t be damaged unless they re going fast enough. There is a minimum amount of energy which colliding particles need in order to react with each other. If the colliding particles have less than this minimum energy then they just bounce off each other and no reaction occurs. This minimum energy is called the activation energy. Page 2

3 Part C: How to speed up a reaction: How can we make a reaction go faster?? The 6 Factors Affecting Rate of Reaction: 1. Temperature: A. How does the temperature increase impact the speed of molecules? Temp KE collisions rate of reaction **Not only is there a higher probability of the molecules colliding, but they re going faster, so it s more likely that when they collide they ll have enough energy to react.** 2. Concentration What happens to the rate of reaction if we increase the concentration of our reactants? Dilute Concentrated concentration collisions rate of reaction 3. Pressure (in gases) 1. What is the relationship between volume and pressure? 2. If you have the same number of gas particles in a smaller volume, what happens to the concentration? Increasing the pressure of a reaction where the reactant is a gas is similar to increasing the concentration of a reactant in a solution. The gas particles will be closer together when the pressure increases. This means that the particles collide more frequently with each other and the rate of the reaction increases. P V concentration collisions rate of reaction Page 3

4 4. Surface Area What if you take a tablet and crush it up. Will the reaction be faster for the tablet or the crushed tablet? Why? 5. Catalyst surface area interaction between particles collisions rate of reaction Definition: A catalyst is a substance that increases the rate of a chemical reaction without getting used up in the reaction. A catalyst can increase the rate of a reaction by offering a different pathway with lower activation energy for the reactants to become products. A catalyst that s in your body is called an enzyme. An example: If your body were to convert food to energy without an enzyme, it would take 3 weeks per bagel! The enzymes in your stomach bring that down to mere hours! Make your own example: 6. Nature of the Reactants There is one more factor to take in to account when you re considering the speed of a reaction, and that s the nature of the reactants. It makes a difference as to whether your reactants are ionic or covalent, and what state of matter they re in. 1. If we want a reaction to happen as fast as possible we need as many collisions between the reactants as possible which state of matter would be best for this? Why? 2. We don t typically work with gases though since they re hard to contain, so which state of matter is the next best? Why? So that s why reactions are usually done in aqueous solutions. 3. So we would rather work with liquids than solids for obvious reasons, but what about ionic vs. covalent? 4. What about the complexity of reactants? Page 4

5 5. For each option of possible reactants, which two would react with each other the fastest. 1) NaCl (s), C 6H 12O 6 (aq), ZnO (l), LiBr (aq) 2) HCl (l), MgO (aq), BaO (s) Page 5

6 Potential Energy Diagrams Name: Date: Period: Part A: Potential Energy Diagrams What is a potential energy diagram? Tracing the reaction 1. The reactants contain a specific amount of energy (Potential Energy). 2. Additional energy is absorbed by the reactants and serves to break certain bonds and initiate the reaction (activation energy). 3. As the reactants absorb energy, they re transformed into an intermediate known as the activated complex. 4. As the activated complex is converted into products, new bonds are formed and energy is released. 5. The products contain a specific amount of energy (Potential Energy of Products). 6. The difference between the energy of the products and the energy of the reactants is the heat of reaction, H. Part B: Exothermic Reaction (Reactants Products + Heat Energy) Since more energy is released than absorbed, the products are at a lower energy state than the reactants = exothermic. The difference between the energy of the products and the energy of the reactants is the heat of reaction, H, which is negative. What is the energy of the reactants? What is the energy of the products? What is the heat of the reaction for the diagram on the right? Part C: Endothermic Reaction ( Heat Energy + Reactants Products) The sequence of events is exactly the same as in an exothermic reaction, but: At the end of the reaction, less energy is released than absorbed and the products are at a higher energy state than the reactants. What is the energy of the reactants? What is the energy of the products? What is the heat of the reaction for the diagram on the right? Page 6

7 Part D: Drawing your own Potential Energy Diagram Draw potential energy diagrams for endothermic and exothermic reactions : Page 7

8 Part E: Catalysts Remember also that a catalyst will lower the activation energy of thereaction, but it does not alter the potential energy of the reactants or products. Remember, catalysts are like match.com they help bring the reactants together, but are not changing the reactants nor the products at the end. They just make it easier to happen! Label the following: 5: Energy of the reactants: add onto diagram Energy of the products: add onto diagram How did the catalyst change the path of the reaction? Part F: Let s try some practice problems using the diagram 1. How much potential energy do the reactants have? 2. How much potential energy do the products have? 3. What is H? 4. Is this reaction endothermic or exothermic? 5. What is the activation energy of the reaction? 6. What type of chemical reaction is this? 7. What would the curve look like if a catalyst was added? Page 8

9 LE CHATELIER s PRINCIPLE Name: Date: Period: Part A: Le Chatelier s Principle Equilibrium How can we write an equilibrium expression for a chemical equation? Remember, a system (or reaction) at equilibrium is one that has the same rate of the forward reaction as the reverse reaction. EVERYTHING IS IN BALANCE!!!! Explains HOW A SYSTEM WILL RESPOND TO. STRESS = Any change in,, or put upon a system at equilibrium. When a is added to a system at equilibrium, the system will in order to relieve that stress and reach a new equilibrium. SHIFT = an increase in the of EITHER the forward OR the reverse rxn Page 9

10 Part B: Shifts Use your pencil to create a balance - Since equilibrium has equal forward and reverse rates, and is in a BALANCE, we can represent it with your pencil or pen. Equilibrium More on the right More on the left Balanced Too many PRODUCTS Too many REACTANTS How do you make it go back to equilibrium??? If we shift it: Then, the reaction will favor: So, LeChatelier s principle tells us how each type of stressor would affect how the equilibrium is reestablished. We are going to look at the different stressors and how they impact the LEFT or RIGHT shift to get back to EQUILIBRIUM. Page 10

11 Part C: Different Types of Stresses: A. CONCENTRATION as a stressor. When the concentration of a reactant or a product is changed, the system will shift in order to restore the original concentration as closely as possible. - Increasing the concentration of one substance, causes the reaction to shift in the opposite direction. (Favors the opposite reaction) - Decreasing the concentration of one substance, causes the reaction to shift in the direction where the concentration decreased. (To make up for the amount lost) Adding concentration: 4NH 3(g) + 5O 2(g) 4NO(g) + 6H 2O(g) + HEAT 1. If we add H 2O(g), the system would shift to the and the [NH 3] would. 2. If we add O 2(g), the system would shift to the and the [NO] would. 3. If we add H 2O(g), the system would shift to the and the [NO] would. 4. If we added NO(g), which concentration(s) would decrease?. Removing concentration: 4NH 3(g) + 5O 2(g) 4NO(g) + 6H 2O(g) + HEAT 1. If we remove oxygen, the system will shift to the and the [NH 3] will. 2. If we remove water, the system will shift to the and the [NO] will. 3. If we remove ammonia, which concentration(s) will decrease?. 4. If we remove NO(g), which concentration(s) would increase?. B. TEMPERATURE: as a stressor: involves increasing or decreasing the HEAT component of a reaction. NOTE: HEAT/ENERGY/J/KJ will either be a reactant or a product A + B C + D + HEAT A + B + energy C + D Heat is a Heat is a Circle one: Exothermic / Endothermic Exothermic / Endothermic When temperature (or HEAT) is changed: Heat is just like concentration. Is it a reactant or a product? Which way will it shift? Adding heat: 4NH 3(g) + 5O 2(g) 4NO(g) + 6H 2O(g) + HEAT 1. Is this reaction exothermic or endothermic? 2. If we added heat, which concentration(s) will decrease? 3. If we added heat, which concentration(s) will increase? Removing heat: CO 2(g) + H 2O(l) kj CH 4(g) + 2O 2(g) 1. Is this reaction exothermic or endothermic? 2. If we remove heat, which concentration(s) will decrease? 3. If we remove heat, which concentration(s) will increase? Page 11

12 C: PRESSURE: as a stressor: Recall, pressure affects ONLY! So every other state (s, l, aq) in the reaction is UNAFFECTED for this type of stress - INCREASE PRESSURE: rxn shifts to side with # GAS MOLECULES (or least # moles of gas) - DECREASE PRESSURE: rxn shifts to side with # GAS MOLECULES (or greater # moles of gas) NOTE: If the rxn contains NO GAS MOLECULES or if the rxn has the SAME # GAS MOLECULES on each side, there is NO EFFECT and NO SHIFT results from an increase or decrease in pressure Gas versus other types of physical states: CO 2(g) CO 2(aq) 1. If we increase the pressure, the concentrations of which species will increase? 2. If we increase the pressure, the concentrations of which species will decrease? 3. If we decrease the pressure, the concentrations of which species will increase? 4. If we decrease the pressure, the concentrations of which species will decrease? Gas molecules on both sides: N 2(g) + 3H 2(g) 2NH 3(g) 1. If we increase the pressure, in which direction will the equilibrium shift? (Count moles of gases on each side 1 st ): 2. If we increase the pressure, the concentration of which species will increase initially? 3. If we decrease the pressure, the concentration of which species will decrease initially? 5. If we decrease the pressure, the concentration of which species will increase initially? Part D: 1. Here s a biological example of an application of Le Chatelier s principle: Hemoglobin (Hb) reacts with oxygen to form HbO2, a substance that transfers oxygen to the tissues in the body. Carbon monoxide (CO) also reacts with HbO2 by the process below. HbO 2(aq) + 4CO(aq) Hb(CO) 4(aq) + O 2(aq) A. Use LeChatelier s Principle to explain why inhaling CO can cause death. B. Use LeChatelier s Principle applied to this equation to suggest a treatment for a victim of CO poisoning. Explain how your treatment affects the equilibrium above. Page 12