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Chemical Kinetics

Chemical Kinetics. Lab 9. Outline. Purpose Today’s Reaction(s) Kinetics Reactions and Reaction Rates Reaction Plots Zero Order Reactions First Order Reactions Second Order Reactions Procedure Precautions Following Lab Reminder. Purpose.

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Chemical Kinetics

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  1. ChemicalKinetics Lab 9

  2. Outline • Purpose • Today’s Reaction(s) • Kinetics • Reactions and Reaction Rates • Reaction Plots • Zero Order Reactions • First Order Reactions • Second Order Reactions • Procedure • Precautions • Following Lab Reminder

  3. Purpose This lab will help you explore the meaning of the term chemical kinetics. You will be able to use this knowledge to evaluate the rate law for one reactant from graphical relationships generated from the changing concentration of the reactant over time.

  4. Reaction(s) 5 SO32-(aq) + 2 IO3-(aq) + 2 H+(aq)→ I2(aq) + 5 SO42-(aq) + H2O(aq) starch(aq) + I2(aq)→ starchI2· complex

  5. Kinetics • Explores the steps by which a reaction takes place • The main step by which a reaction takes place is described by a rate law of the rate-limiting step of the reaction. • The rate is studied only under forward conditions and is determined by the number of effective collisions and the energy per collision.

  6. Reactions and Rates • Effective collisions must occur with the correct orientation of species and sufficient energy • The reaction could be facilitated or inhibited by molecular / ionic structure. • The rate of a reaction is affected by these things (among others): • Temperature • Concentration • Presence or absence of a catalyst

  7. Procedure 1. Determine the reaction order of the reaction with respect to the iodate ion • Find the reaction times of six solutions by varying the [IO3-], but holding the [SO32-] constant. • Determine the reaction order by finding the linear plot. • Determine the reaction order of the reaction with respect to the sulfite ion. (Beyond the scope of this class.) • Combine rate laws to determine the overall reaction order and rate law. (Beyond the scope of this class.)

  8. Concentration Decay CurveThe shape (and function) of this curve depends on the order of the reaction. T0 T1 T2 T3 T4 T5 T6

  9. Reaction Plots • To determine which reaction order a reaction follows, and therefore, which rate law a reaction obeys, we plot three different graph types for each reagent participating in the reaction. • Whichever graph yields a linear response dictates the reaction order and rate law to be used.

  10. Zero Order Reaction • Linear when [x], M vs. Time,s is plotted. • k = -m; In this case k = 0.0100 • Rate Law: Rate = k[x]0 = k; In this case Rate = 0.0100

  11. First Order Reaction • Linear when ln [X] vs. Time,s is plotted. • k = -m; In this case k = 0.0332 • Rate Law: Rate = k[A]1= k[A] ; In this case Rate = 0.0332[X]

  12. Second Order Reaction • Linear when 1/[X], 1/M vs. Time, s is plotted. • k = m; In this case k = 0.0225 • Rate Law: Rate = k[A]2; In this case Rate = 0.0225[X]2

  13. Rate Laws • A rate law is a mathematical description of a reaction rate’s dependence on concentration. • When you identify the rate law for your reaction, be sure to substitute in a value for k and an identity for the A in [A].

  14. Procedure 1. Determine the reaction order of the reaction with respect to the iodate ion • Find the reaction times of six solutions by varying the [IO3-], but holding the [SO32-] constant. • Determine the reaction order by finding the linear plot. • Determine the reaction order of the reaction with respect to the sulfite ion. (Beyond the scope of this class.) • Combine rate laws to determine the overall reaction order and rate law. (Beyond the scope of this class.)

  15. Safety Concerns • Reagents: • Potassium Iodate (0.1 N) • Potassium Sulfate • Sodium Sulfite • Soluble Starch • Sulfuric acid (0.1 N) • Eye Contact: • Irritation, redness, burns, pain, and irreversible damage. • Skin Contact: • Irritation, redness, burns and pain. • Inhalation: • Coughing, sneezing, sore throat, labored breathing, burns, delayed lung edema and chest pain. • Ingestion: • Nausea, vomiting, diarrhea, gastric irritation, circulatory disturbances, and CNS depression

  16. Precautions • Solutions will be acidic once they are made. Do not dispose of any of them down the sink. They need to go in the acid waste container in the fume hood. • Iodine stains clothing and skin! Be careful when working with your solutions today. Wear gloves if you’d like to protect your hands.

  17. Lab 10 Reminder • Lab 10 is next.

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