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Unit 9A: Kinetics and Energy Changes Unit 9: Kinetics, Thermodynamics, & Equilibrium-Lecture Regents Chemistry ’14-‘15 Mr. Murdoch Unit 9a: Kinetics and Energy Changes 1. Student Name: _______________________________________ Class Period: ________ Unit 9a (Kinetics & Energy Changes) Page 1 of 43 Unit 9: Kinetics, Thermodynamics, & Equilibrium-Lecture Regents Chemistry ’14-‘15 Mr. Murdoch Page intentionally blank Unit 9a (Kinetics & Energy Changes) Page 2 of 43 Unit 9: Kinetics, Thermodynamics, & Equilibrium-Lecture Regents Chemistry ’14-‘15 Mr. Murdoch Unit 9 Vocabulary: 1. Activated Complex: The species that are formed and decomposed during the mechanism; also called the intermediate. 2. Activation Energy: The energy that must be added to allow the reactants to start the reaction and form the activated complex. 3. Catalyst: A chemical that is added to a reaction to eliminate steps in the mechanism, increase the reaction rate, and decrease the activation energy without itself being consumed by the reaction. 4. Effective Collision: A collision between reactant particles that results in a chemical reaction taking place. 5. Enthalpy: The total amount of potential energy stored in a substance. 6. Endothermic: A reaction that absorbs and stores energy from the surrounding environment. 7. Entropy: A system’s state of disorder. Entropy increases as temperature increases. Entropy increases as a substance goes from solid to liquid to gas. 8. Equilibrium: A system where the rate of forward change is equal to the rate of reverse change. At equilibrium there is no net change. 9. Exothermic: A reaction that releases stored energy into the surrounding environment. 10. Favored: A change in a thermodynamic property that contributes towards the reaction being spontaneous. 11. Gibbs Free Energy: The total amount of energy available in a system to do work. Free Energy is a combination of both enthalpy and entropy. 12. Heat of Reaction: The net gain or loss of potential energy during a chemical reaction. 13. Inhibitor: A chemical that is added to a reaction to add steps to the mechanism, decrease the reaction rate, and increase the activation energy without itself being consumed by the reaction. 14. Kinetics: The study of reaction mechanisms and reaction rates. 15. Nonspontaneous: A reaction that requires a constant input of energy to occur, or the reaction will reverse or stop. Unit 9a (Kinetics & Energy Changes) Page 3 of 43 Unit 9: Kinetics, Thermodynamics, & Equilibrium-Lecture Regents Chemistry ’14-‘15 Mr. Murdoch 16. Reaction Rate: The amount of reactant consumed in a given unit of time. 17. Spontaneous: A reaction that continues independently once started. 18. Thermodynamics: The study of heat flow during physical and chemical changes. 19. Unfavored: A change in a thermodynamic property that contributes towards the reaction being nonspontaneous. Unit 9a (Kinetics & Energy Changes) Page 4 of 43 Unit 9: Kinetics, Thermodynamics, & Equilibrium-Lecture Regents Chemistry ’14-‘15 Mr. Murdoch Notes page: Unit 9a (Kinetics & Energy Changes) Page 5 of 43 Unit 9: Kinetics, Thermodynamics, & Equilibrium-Lecture Regents Chemistry ’14-‘15 Mr. Murdoch Unit 9a Homework Assignments: Assignment: Date: Due: Unit 9a (Kinetics & Energy Changes) Page 6 of 43 Unit 9: Kinetics, Thermodynamics, & Equilibrium-Lecture Regents Chemistry ’14-‘15 Mr. Murdoch Topic: Kinetics Objective: How do reactions occur, and how fast do they occur? Chemical Kinetics: Chemical Kinetics are the study of: i. Reaction mechanisms (how reactions occur) and; ii. Reaction rates (how long the reaction takes to complete). Mechanism: A mechanism is the pathway the reaction takes. i. Each mechanism is a series of steps that leads from reactants to products; ii. Particles of reactant material must collide to react; iii. Collisions must occur with enough activation energy to react; iv. Molecules must be orientated (positioned) properly to react. Collisions that satisfy these requirements and lead to the initiation of the reaction are labeled effective collisions. The effective mechanism can occur in a series of steps, each involving electron shifts as old bonds are broken and new bonds are formed. How to speed up chemical reactions (and get a date) - Aaron Sams - YouTube - 4:56 Unit 9a (Kinetics & Energy Changes) Page 7 of 43 Unit 9: Kinetics, Thermodynamics, & Equilibrium-Lecture Regents Chemistry ’14-‘15 Mr. Murdoch Topic: Kinetic Mechanisms Objective: What types of steps may make a reaction mechanism? Reaction Example: CO(g) + NO2(g) CO2(g) + NO(g) This reaction does NOT go directly as stated above. It first starts with the decomposition of nitrogen dioxide. Step #1: 2 NO2(g) NO3(g) + NO(g) Step #2: CO(g) + NO3(g) CO2(g) + NO2(g) Final step: CO(g) + NO2(g) CO2(g) + NO(g) Reaction Example (Reference Table I): H2 + I2 2 HI For the reaction above, a possible reaction might be: 1. Step #1: H2(g) 2 H(g) (the covalent bond in the diatomic hydrogen molecule absorbs energy to break apart into hydrogen atoms; 2. Step #2: I2(g) 2 I(g) (the covalent bonds in the diatomic iodine molecule absorb energy to break apart into iodine atoms; 3. Step #3: 2 I(g) + 2 H(g) 2 HI(g) (H would rather bond to I than H - electronegativity). New H-I bonds form, releasing energy; 4. Net Reaction: H2(g) + I2(g) 2 HI(g) (2 H and 2 I are intermediates (activated complex) formed in steps #1 & #2, which are then used in step #3. Unit 9a (Kinetics & Energy Changes) Page 8 of 43 Unit 9: Kinetics, Thermodynamics, & Equilibrium-Lecture Regents Chemistry ’14-‘15 Mr. Murdoch Topic: Kinetic Mechanisms Objective: What types of steps may make a reaction mechanism? Reaction mechanisms: A reaction mechanism is similar to different roads that lead to the same destination. Depending on which road taken, it requires a different amount of time and/or energy to reach your destination. The only way to learn exactly which mechanism is truly responsible for the reaction occurring is to complete an experiment. The overall rate of any mechanism is determined by the slowest step in the mechanism. o The slowest step is the rate-limiting step or rate-determining step. For any reaction, whichever step is the slowest is the part of the mechanism that controls the speed of the overall reaction. Watch Bozeman Chemistry The Rate-Limiting Step - YouTube - 6:46 Unit 9a (Kinetics & Energy Changes) Page 9 of 43 Unit 9: Kinetics, Thermodynamics, & Equilibrium-Lecture Regents Chemistry ’14-‘15 Mr. Murdoch Topic: Catalysts Objective: How might we increase the rate of a reaction? Catalysts: A catalyst is something that speeds up a reaction by modifying a step in the reaction mechanism with the result being a shortened mechanism. i. A catalyst generally lowers the activation energy required to initiate a mechanism, or a step in a mechanism, allowing the overall reaction to proceed at a faster rate. ii. Catalysts are not consumed by the reaction. A catalyst becomes a temporary part of the mechanism, then is released, and is able to work again within the mechanism. iii. When you dissolve an ionic solid (crystal) in water to form an aqueous ionic solution before undergoing a double replacement reaction, the water acts as a catalyst as the moving water molecules increase the rate that the dissolved ions will collide. Faster collisions = faster reactions! Unit 9a (Kinetics & Energy Changes) Page 10 of 43 Unit 9: Kinetics, Thermodynamics, & Equilibrium-Lecture Regents Chemistry ’14-‘15 Mr. Murdoch Topic: Inhibitors Objective: How might we decrease the rate of a reaction? Inhibitor: An inhibitor is something that slows down a reaction by adding additional steps to the mechanism with the result generally lengthening the amount of time needed for the reaction to complete. i. Inhibitors generally increase the activation energy; if you require more energy to initiate a reaction, it will take longer to add that extra energy. ii. Inhibitors are not consumed by the reaction. iii. Certain non-ferrous metals form a patina (a combination of oxides, carbonates, or sulfides) that will inhibit additional oxygen from gaining access to the metal and causing further oxidation. The Statue of Liberty is made of copper sheets; the green color we see is the result of oxygen reacting with the copper and forming the greenish patina. Unit 9a (Kinetics & Energy Changes) Page 11 of 43 Unit 9: Kinetics, Thermodynamics, & Equilibrium-Lecture Regents Chemistry ’14-‘15 Mr. Murdoch Topic: Reaction Rates Objective: How do we measure the amount of a reaction over time? Reaction Rate: The speed at which a reactant is chemically changed into a product is known as the Reaction Rate. i. The rate of reaction is generally measured in terms of amount of reactants consumed over a period of time. ii. Reaction rate is measured by the number of effective molecular collisions that occur per unit of time. The greater the number of effective collisions in a period, the faster the reaction rate. iii. Any action that speeds up the rate of effective collisions will increase the rate of the reaction. Unit 9a (Kinetics & Energy Changes) Page 12 of 43 Unit 9: Kinetics, Thermodynamics, & Equilibrium-Lecture Regents Chemistry ’14-‘15 Mr. Murdoch Topic: Rate and Reactant Nature Objective: How may the type of reactants change reaction rate? Ionic Reactions: 1. Ionic reactions occur quickly; 2. Ionic reactions occur in liquid water, and the nature of liquid water allows a large number of collisions in aqueous solution; 3. Aqueous solutions of ions have the ionic bonds already broken, and they can readily make new ionic bonds; 4. Precipitate reactions occur almost immediately upon mixing solutions. Covalent reactions: 1. Covalent reactions occur slowly; 2. Covalently bonded molecules have many different types of bonding, and that can make some covalent reactions very slow; 3. Covalently bonded molecules may have single, double, or even triple bonds that require large amounts of energy to break; 4.
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