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Kinetics Rates of Chemical Reactions

Kinetics Rates of Chemical Reactions. Dr. Ron Rusay. A  B. Chemical Reactions: Time & Progress. Red  Blue. t (min). 100 molecules. 54 Red : 46 Blue. 30 Red : 70 Blue. A  B. Moles A & B vs. Time. QUESTION.

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Kinetics Rates of Chemical Reactions

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  1. Kinetics Rates of Chemical Reactions Dr. Ron Rusay

  2. A  B Chemical Reactions:Time & Progress Red  Blue t (min) 100 molecules 54 Red : 46 Blue 30 Red : 70 Blue

  3. A  B Moles A & B vs. Time

  4. QUESTION If we have the reaction A(g)  2B(g) and the number of moles of A follows: time 0 5 min 10 min moles A 0.100 0.085 0.070 What is the number of moles of B at 10 min? •   0.060 mol •   0.200 mol •   0.140 mol •   0.100 mol •   0.030 mol

  5. ANSWER If we have the reaction A(g) 2B(g) and the number of moles of A is as follows, time 0 5 min 10 min moles A 0.100 0.085 0.070 What is the number of moles of B at 10 min? • 0.060 mol •   0.200 mol •   0.140 mol •   0.100 mol •   0.030 mol 0.100 molA -0.070 molA 0.030 molA x 2 molB/1molA

  6. CONSIDER RATE of change for: A  B

  7. Expressions of a Rate of Reaction For the Chemical Reaction:aA + bB cC + dD

  8. QUESTION Chlorine dioxide (ClO2), a yellow-green gas, which dissolves in water, is used as a disinfectant in some municipal water-treatment plants. In a basic aqueous solution, it produces chlorate ion, ClO3–, and chlorite ion, ClO2–: 2 ClO2(aq) + 2 OH– (aq)  ClO3– (aq) + ClO2– (aq) + H2O (l) Of the following choices, which would not be a correct expression to relate the rate of the reaction relative to concentration changes of different reactants and products? –DClO2/Dt = 2DClO3–/Dt –DClO2/Dt = DOH–/Dt –DClO2/Dt = DClO2–/Dt –DOH–/Dt = 2DClO2–/Dt

  9. QUESTION Chlorine dioxide (ClO2) is a disinfectant used in municipal water-treatment plants. It dissolves in basic solution producing ClO3– and ClO2–: 2ClO2 (aq) + 2OH– (aq)  ClO3– (aq) + ClO2– (aq) + H2O (l) Of the following, which would not be a proper expression to relate information about the rate of the reaction? –DClO2/Dt = 2DClO3–/Dt –DClO2/Dt = DOH–/Dt –DClO2/Dt = DClO2–/Dt –DOH–/Dt = 2DClO2–/Dt

  10. ANSWER C. The stoichiometry of the reaction indicates that ClO2 disappears twice as fast as ClO2– forms; so to determine the rate for ClO2 , the rate of ClO2– would have to be doubled or ½ of the rate of disappearance of ClO2.

  11. Rate of Reaction • C4H9Cl(aq) + H2O(l)  C4H9OH(aq) + HCl(aq) • The average rate can be expressed in terms of the disappearance of C4H9Cl. • The units for average rate are mol/L.s or M/s. • The average rate decreases over time.

  12. Rate of Reaction • C4H9Cl(aq) + H2O(l)  C4H9OH(aq) + HCl(aq) • Data and plotting [C4H9Cl] versus time:

  13. Rate of Reaction • C4H9Cl(aq) + H2O(l)  C4H9OH(aq) + HCl(aq) • The rate at any instant in time (instantaneous rate) is the slope of the tangent to the curve @ a time (s). • Instantaneous rate is different from average rate.

  14. http://chemconnections.org/general/movies/Ea-1.MOV Ea-2.MOV Ea-3.MOV

  15. Indicator Kinetics Color Changes & Concentrations Gram-positive bacteria take up the crystal violet & stain purple Crystal Violet + OH- Phenolphthalein + H2O -

  16. Important Factors that Effect Reaction Rates 1) Concentration:molecules must collide in order to react. The higher the concentration, the higher number of collisions. Rate = k (collision frequency) = k (concentration) k = rate constant 2) Physical state:molecules must physically mix in order to collide. The physical state (solid, liquid, gas) will affect frequency of collisions, as well as the physical size of droplets (liquid) or particles in the case of solids.(heterogeneous vs. homogeneous) 3) Temperature:molecules must collide with enough energy to react. (Activation Energy, Ea) Raising the temperature increases the K.E. of the molecules, the number of collisions and the energy of the collisions.

  17. Temperature: molecules must collide with enough energy to react. (Activation Energy, Ea) Raising the temperature increases the K.E. of the molecules, the number of collisions and the energy of the collisions.

  18. QUESTION • Which line in the Energy Diagram corresponds to the activation energy for the forward reaction? • X • Y • Z • W

  19. ANSWER • Which line in the Energy Diagram corresponds to the activation energy for the reverse reaction? • X • Y • Z • W

  20. QUESTION • Which line in the Energy Diagram corresponds to the activation energy for the reverse reaction? • X • Y • Z • W

  21. ANSWER • Which line in the Energy Diagram corresponds to the activation energy for the reverse reaction? • X • Y • Z • W

  22. QUESTION Which of the following is a correct conclusion based on the information presented in this figure? The forward reaction is endothermic. The activation energy for the forward reaction is less than the activation energy of the reverse reaction. The transition state is at a lower energy than the products. The energy of the reactants represents a lower energy level than both the transition state and the products.

  23. ANSWER B. The activation energy of the forward reaction is lower than the reverse. From the reactants to the transition state the energy change is less than from the products to the transition state.

  24. https://phet.colorado.edu/en/simulation/legacy/reactions-and-rateshttps://phet.colorado.edu/en/simulation/legacy/reactions-and-rates PhET Simulation

  25. Catalysts Alternative Reaction Pathways • Catalysts increase reaction rates by lowering the Energy of Activation Ea vs Ea • Catalysts are not consumed in chemical reactions

  26. QUESTION The second diagram in this figure does not support the statement … That the catalyst increases the number of effective collisions. That the reaction rate will be lower without the catalyst. That adding a catalyst decreases Ea, the Energy of Activation. That the catalyst can provide an alternate reaction pathway, which would increases the effective collisions and increase the reaction rate.

  27. ANSWER The second diagram in this figure does not support the statement … That the catalyst increases the number of effective collisions. That the reaction rate will be lower without the catalyst. That adding a catalyst decreases Ea, the Energy of Activation. That the catalyst can provide an alternate reaction pathway, which would increases the effective collisions and increase the reaction rate.

  28. Enzymes Catalytic Power Enzymes lower the Energy of Activation and dramatically increase the reaction rate.

  29. Enzymes Catalytic Power • Enzymes can accelerate reactions as much as 1016 times over uncatalyzed rates, i.e., 10,000,000 billion times! • Urease: (Found in bacteria, yeast & higher plants) • Breaks down urea into ammonia, CO2 and releases energy. • Catalyzed rate: 3 x 104/sec • Uncatalyzed rate: 3 x 10-10/sec • Relative difference is 1 x 1014 (100,000 billion times)

  30. HumanMetabolismDefined by enzymes:globular proteins that catalyze all reactions & processes in human chemical biology

  31. Avadine: anti-diabetes drug tested in mice triggersenzymatic conversion of white fat to energy burning brown

  32. What is a fat? Common Functional Groups NameGeneral Formula Alcohols R Ethers RR Amines RNH2 Carboxylic “Fatty” Acids R contains 3 (–OH) groups in totalglycerol + fatty acid (R is very large and has an even number of carbon atoms)

  33. What is a fat? Common Functional Groups NameGeneral Formula Aldehydes Ketones Carboxylic “Fatty” Acids Esters Amides (R is very large) (R is very large; R’ is glycerol; triglycerides)

  34. Molecular Formula: C57H110O6 Molecular weight: 891.4797 kJ/mol

  35. Structure of a mixed triacylglycerol in which three different fatty acid residues are present. Saturated Mono-unsaturated (cis) Polyunsaturated (cis)

  36. The melting point of a fatty acid depends on the length of the carbon chain and on the number of double bonds present in the carbon chain.

  37. How do fat molecules differ?

  38. http://chemconnections.org/general/movies/fat-satd.MOV http://chemconnections.org/general/movies/fat-unsatd.MOV

  39. http://chemconnections.org//general/chem106/The%20Worst%20Fat%20in%20the%20Food%20Supply%20-%20The%20New%20York%20Times.pdfhttp://chemconnections.org//general/chem106/The%20Worst%20Fat%20in%20the%20Food%20Supply%20-%20The%20New%20York%20Times.pdf

  40. Question Which of the following statements regarding fatty acids is false? A) Fatty acid can have one or more carbon-carbon double bonds. B) Naturally occurring fatty acids have an odd number of carbons. C) The configuration of the double bond(s) is (are) generally cis in naturally occurring fatty acids. D) Unsaturated fatty acids have a lower melting point than saturated ones.

  41. Answer Which of the following statements regarding fatty acids is false? A) Fatty acid can have one or more carbon-carbon double bonds. B) Naturally occurring fatty acids have an odd number of carbons. C) The configuration of the double bond(s) is (are) generally cis in naturally occurring fatty acids. D) Unsaturated fatty acids have a lower melting point than saturated ones.

  42. Enzyme:AMPK + Activator AMPK converts white fat where lipids store energy to brown fat which burn lipids to produce heat (energy).

  43. Human Circadian Rhythm & Oscillating Reactions At what time of day will most people produce urine at the fastest rate? At what time of day will you most likely have an allergic reaction? ~6:00 PM ~11:00 PM http://www.sciencedirect.com/science/article/pii/0021870765900869

  44. Oscillating Reactions & Bio Feedback Bread mold cycle: WC-1 = (+8 hrs to recycle) Bread mold cycle: frq = ( +16 hrs to recycle) J. Arnold, Proc. Natl. Acad. Sci., 104, 2809-2814, Feb. 27, 2007. http://www.pnas.org/content/104/8/2809.full

  45. Enzymes Function& Inhibition • Competitive inhibition: Inhibitor (I) binds only to E, not to ES. (Substrate cannot bind.) • Noncompetitive inhibition: Inhibitor (I) binds either to E and/or to ES. (Can increase, decrease or remain constant.) http://chemconnections.org/general/movies/Enzymes-Energy.mov

  46. Reaction Rate Expression / Rate Law For a Chemical Reaction:aA + bB cC + dD A Rate Expression for this reaction could be written as: Rate = k [A]m[B]n . . . k = the reaction rate constant m & n are called reaction orders. They define how the rate is effected by the concentration of each reactant, for example, if the rate doubles when the concentration of A doubles, the rate depends on [A]1, so a = 1; if the rate quadruples when the concentration of B doubles, the rate depends on [B]2, so b = 2. Can a reaction order equal zero? Yes, for Rate = k [A]m = 0 Rate = k

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