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Typical Graphs

Typical Graphs . Rate of Reaction = Chemical Kinetics. Δ [Concentration]. Δ Time. Rate of Rxn = = Slope. Reaction Rates. Rates of reactions can be determined by monitoring the change in concentration of either reactants or products as a function of time . Watch This!.

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Typical Graphs

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  1. Typical Graphs

  2. Rate of Reaction = Chemical Kinetics Δ [Concentration] Δ Time • Rate of Rxn = = Slope

  3. Reaction Rates Rates of reactions can be determined by monitoring the change in concentration of either reactants or products as a function of time.

  4. Watch This!

  5. Par Example C4H9Cl(aq) + H2O(l) C4H9OH(aq) + HCl(aq) In this reaction, [the concentration]of butyl chloride, C4H9Cl, was measured at various times.

  6. Average rate = Average rate = [.10 - .0905] [50 – 0] [C4H9Cl] t Reaction Rates The average rate of the reaction over each interval is the change in concentration divided by the change in time: = 1.9 x 10 -4

  7. AVERAGE RATE CHANGES! • It is not constant. • What’s happening to the average rate?

  8. Practice Example 14.1 p. 560

  9. Reaction Rates • Note that the average rate decreases as the reaction proceeds. • This is because as the reaction goes forward, there are fewer collisions between reactant molecules.

  10. Change of Rate over Time Practice Example p. 598 #14.4 YES! Linear Function with positive slope. b. Yes! The slope = 0 indicating that the reaction is over evidenced by no change in [M].

  11. Instantaneous Rate of Change • Instantaneous Rate of Change = slope of tangentline to curve at a point “t” @ t = 0, initial rate

  12. Think of it this way! • Your instantaneous rate is • You drove 98 miles to Charlotte in 2 hours. • Your average rate is 49 mi/hr.

  13. Reaction Rates p. 561 C4H9Cl(aq) + H2O(l) C4H9OH(aq) + HCl(aq) • A plot of [C4H9Cl] vs. time for this reaction yields a curve like this. • The slope of a line tangent to the curve at any point is the instantaneous rate at that time= RATE @ instant. • Examine the slope at t = 0 vs. slope at t = 600 s. • Which is greater? Steeper Slope

  14. What’s happening over time? Slope is decreasing. Rate is decreasing. Reaction is slowing.

  15. Reaction Rates C4H9Cl(aq) + H2O(l) C4H9OH(aq) + HCl(aq) • All reactions slow down over time. • Therefore, the best indicator of the rate of a reaction is the instantaneous rate near the beginning of the reaction.

  16. How do calculate instantaneous rate? • NON-Calculus Method • Find slope of line at point: HOW??? • USE GRAPH! • Draw in tangent line • Calculate ~ slope • Approximation of actual slope of tangent line to curve @ t = seconds • Calculus Method • In order to find the ACTUAL slope of tangent line at t = X seconds • MUST know function • DON’T know function • IF we knew the function, THEN we could use the 1st derivative to find the actual instantaneous rate of change

  17. Calculus Application First Derivative = slope of tangent line to curve at t = 2 First Derivative = Velocity

  18. Let’s Practice p. 600 #14.21 • (a) Calculate averages between intervals of time. • (b) Calculate average rate over entire time interval. • (c) Use LoggerPro to graph data. Select natural exponent function. • ANSWERS FOUND ON p. A-18 at back of book. AVERAGE = OVER SPECIFIC TIME INTERVAL INSTANTANEOUS = @ SPECIFIC TIME VALUE

  19. -[C4H9Cl] t Rate = = [C4H9OH] t Reaction Rates and Stoichiometry C4H9Cl(aq) + H2O(l) C4H9OH(aq) + HCl(aq) • In this reaction, the ratio of C4H9Cl to C4H9OH is 1:1. • Thus, the rate of disappearance of C4H9Cl is the same as the rate of appearance ofC4H9OH.

  20. 1 2 [HI] t Rate = − = [I2] t Reaction Rates and Stoichiometry What if the ratio is not 1:1? 2 HI(g)  H2(g) + I2(g)

  21. aA + bB cC + dD = − = = Rate = − 1 a 1 b 1 c 1 d [C] t [D] t [A] t [B] t Reaction Rates and Stoichiometry • To generalize, then, for the reaction

  22. Sample Exercise 14.3 p. 563

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