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Kinetics

Kinetics. Further Studies. Quiz. Please take out a piece of blank paper. Place your name and lab day and time at the top. Failure to put your complete identification on the exit quiz will preclude you from attending lab! When you are finished, turn in your quiz to a waiting TA.

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Kinetics

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  1. Kinetics Further Studies

  2. Quiz Please take out a piece of blank paper. Place your name and lab day and time at the top. Failure to put your complete identification on the exit quiz will preclude you from attending lab! When you are finished, turn in your quiz to a waiting TA. • Generally, reaction rate increases/remains unchanged/decreases with decreasing temperature. • What does a catalyst do? Biological catalysts, formed from proteins, are called ___________.

  3. Kinetics Further Studies

  4. Rate Law For a chemical reaction: aA + bB + . . . cC + dD + . . . The rate law for the reaction has the form: Rate = k [A]m[B]n . . . k = the reaction rate constant m & n are the reaction orders which define how the rate is effected by the concentration of each reactant. Note that m and n must be experimentally determined

  5. Methods for determining rate laws • Method of initial rates • Covered in text • Integrated rate laws • e.g., pseudo-first-order kinetics • Next week’s lab • Log graphing • This week

  6. Log Graphing • Limited to rate laws in which only one component changes 2 H2O2(aq) 2 H2O(l) + O2(g)

  7. General form of the rate law: Rate = k[H2O2]m m Now, let’s play a math game to get m and k in as few a number of experiments as possible: [H2O2] log k log Rate = log Rate = + m log which is… why = bee + emex The equation of a straight line!

  8. log Rate = mlog[H2O2] + log k A plot of log Rate vs. log[H2O2] should give a straight line with: slope = m(reaction order) y-intercept = log k (rate constant)

  9. How to track the rate of reaction? • Gas is produced • Could use pressure sensor • Could pass produced gas though a solution and count bubbles

  10. Apparatus Water bath H2O2 solution Catalyst

  11. Lab Notes • Need to prepare a catalyst that will give 2-3 bubbles/second for 5% H2O2 solution • = about 100 mg MnO2 conveniently in a teabag • Need to place 25 mL Erlenmeyer in water bath for constant temp • Analyze 5 solutions from 5%-1% • Do repeat trials • Use same amount of H2O in the pipette each time

  12. Lab Notes • Start collecting data after ~1 min • You choose data collection amount • Reuse and recycle the pyrolusite. • If you lose or damage your bag of pyrolusite, you must start over. • Complete graphs before you leave • Read comments from TA’s

  13. Lab notes This investigation, Author 2: Introduction and Conclusion 3: Discussion 1: Data/Results and Experimental This investigation, Author A: Introduction, Conclusion, Data/Results B: Discussion and Experimental

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