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Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille, Chemistry , 2007 (John Wiley)      ISBN: 9 78047081 0866. CHEM1002 [Part 2]. A/Prof Adam Bridgeman (Series 1) Dr Feike Dijkstra (Series 2) Weeks 8 – 13

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  1. Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille,Chemistry, 2007 (John Wiley)     ISBN: 9 78047081 0866

  2. CHEM1002 [Part 2] A/Prof Adam Bridgeman (Series 1) Dr FeikeDijkstra (Series 2) Weeks 8 – 13 Office Hours: Monday 2-3, Friday 1-2 Room: 543a e-mail:adam.bridgeman@sydney.edu.au e-mail:feike.dijkstra@sydney.edu.au

  3. Summary of Last Lecture • Complexes IV • The metals include many essential elements (such as Na+, K+ and Ca2+, some toxic (such as Hg2+ and Al3+) and some which are now being used in medicines (such as Pt2+) • The essential metals have a variety of functions in the body (such as Na+/K+ in the nervous system, Fe2+/3+ in oxygen transport and Zn2+ in CO2 transport) • The biological function is related to the oxidation number, the coordination type and the size of the atom

  4. Chemical Kinetics I • Lecture 16 • Chemical Kinetics • Rate of Reaction • Rate Laws • Reaction Order • Blackman Chapter 14, Sections 14.1 - 14.3 • Lecture 17 • Half lives • The Temperature Dependence of Reaction Rates • Catalysis • Blackman Chapter 14, Sections 14.4 - 14.6

  5. Thermodynamics (ΔG, ΔunivS, Eo) tells us if a reaction favours the products or reactants It also gives the extent a reaction occurs (Keq) Kinetics vs Thermodynamics • Thermodynamics says nothingabout how fast or slow the reaction goes • It gives us the equilibrium concentrations but not how long it takes to get to equilibrium

  6. The rate of a reaction is how fast the concentration of the molecules present change. Reaction rate: change in concentration of a product or a reactant per unit time. Rate is given by the gradient of concentration vs time graph Reaction Rate d[A]= ——dt reaction rate

  7. Expressing Reaction Rates • There are a number of ways to express the rate. hydrolysis of cisplatin [Pt(NH3)2Cl2] + H2O  [Pt(NH3)2(H2O)Cl]+ + Cl- d[product] d[reactant] — + rate = = dt dt

  8. Express the rate of reaction for each reactant and product in the reaction: 4NH3(g) + 5O2(g)4NO(g)+6H2O (g) 1 1 - + 4 4 1 1 - + 5 6 Expressing Reaction Rates d[NH3] d[NO] NH3: NO: dt dt d[O2] d[H2O] O2: H2O: dt dt

  9. d[O3] fast slow Rates are Determined Experimentally rate = - C2H4 + O3 C2H4O + O2 dt • Rate is dependent of concentration of O3

  10. The Rate Law • The rate of the reaction is proportional to the concentration[O3] and to that of [C2H4] • This is expressed as a rate law: • rate = k[O3] [C2H4] • k is the rate constant and is independent of concentration • kincreases with T

  11. For the general reaction: The Rate Equation aA + bB + cC …  mM + nN …. -d[A] = k [A]x [B]y [C]z … dt • the rate lawcan only be determined by experiment, not from the stoichiometric equation • x is the orderof the reaction with respect to A,y is the orderof the reaction with respect to B… • theoverall order of the reaction is given by x + y + z … • there is no relationship between a and x, b and y ….

  12. Example For the reaction: 2 NO (g) + O2 (g)  2 NO2 (g) rate= k[NO]2[O2] What is the order of reaction withrespect tothe reactants and the overall order of reaction? • secondorder with respect to NO • first order with respect to O2 • third order overall

  13. If x = 1, reaction is 1st order in A: rate α [A]1 If [A] doubles, then rate goes up by factor of 16 Interpreting Rate Laws = k [A]x [B]y [C]z … rate two • If x = 2, reaction is 2nd order in A: rate α [A]2 • If [A] doubles, then rate goes up by factor of four • If x = 3, reaction is 3rd order in A: rate α [A]3 • If [A] doubles, then rate goes up by factor of eight

  14. Using Data to Determine Order ClO3-(aq) + 9 I- (aq) + 6 H+(aq)Cl-(aq) + 3 I3-(aq) + 3 H2O(l) [H+] / M [ClO3-] / M initial rate / M s-1 [I-] / M 1 0.10 0.10 0.10 0.05 2 0.20 0.10 0.10 0.10 3 0.20 0.20 0.10 0.20 4 0.20 0.20 0.20 0.80 rate = k [ClO3-]x [I-]y [H+]z , y = 1 and z = 2 x = 1 so

  15. Using Data to Determine Order Calculate the rate constant, k: in experiment 1: rate = 0.05 M s-1, [ClO3-] = 0.1 M, [I-] = 0.1 M, [H+] = 0.1 M ClO3-(aq) + 9 I- (aq) + 6 H+(aq)Cl-(aq) + 3 I3-(aq) + 3 H2O(l) rate = k [ClO3-] [I-] [H+]2 so, (units of k depend on overall order) 0.05 M s-1 = k(0.10 M)(0.10 M)(0.10 M)2 k = 5.0 x 102 M-3 s-1

  16. Question NO2 (g) + CO (g)NO (g) + CO2 (g) [NO2] / M [CO] / M Initial rate / M s-1 1 0.10 0.10 0.0050 2 0.400.10 0.080 3 0.100.20 0.0050 • determine the rate equation and value of the rateconstant for this reaction rate = k[NO2]2 (zero order in [CO]) k = 0.5 M-1 s-1

  17. Summary: Chemical Kinetics I • Learning Outcomes - you should now be able to: • Work out the order of the reaction with respect to each reactant from experimental data • Work out the rate constant (including its units) from experimental data • Hence, write down the rate law • Answer review problems 14.66 - 14.97 in Blackman • Complete the worksheet • Next lecture: • Half lives, temperature dependence and catalysis

  18. Practice Example

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