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Understanding reaction mechanisms (an analogy)

Describes in great detail the order in which bonds are broken and formed and the changes in relative position of the atoms during the course of reaction. Understanding reaction mechanisms (an analogy).

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Understanding reaction mechanisms (an analogy)

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  1. Describes in great detail the order in which bonds are broken and formed and the changes in relative position of the atoms during the course of reaction.

  2. Understanding reaction mechanisms (an analogy)

  3. The slowest step in this sequence will determine how fast you can get to school (product). Waking up may be the slow step for some while taking a shower may be the slow step for others. --Speeding up the slow step will speed up the overall reaction. If for example taking a shower was the slow step you might shower the night before and simply wash your face in the morning. --If taking the bus is the slow step you might get a ride with a friend that might be quicker and therefore speed up the mechanism. THE SLOW STEP IS THE RATE DETERMINING STEP!

  4. A Reaction mechanism is a series of elementarysteps that must satisfy two requirements: 1. The sum of the elementary steps must give the overall balanced equation for the reaction. 2. The mechanism must agree with the experimentally determined rate law.

  5. Consider a Chemical reaction:

  6. Definitions

  7. Overall An INTERMEDIATE is formed in one elementary step and consumed in the next. Multistep mechanisms can have more than one intermediate.

  8. Let’s consider the Reaction between Hydrogen gas and Iodine 1) Write out the three steps in this reaction mechanism: 2) What is the Overall reaction? 3. List the intermediate substances in this reaction mechanism. I2 --> I + I I + H2 --> H2I H2I + I --> 2HI H2 + I2 --> 2HI I and H2I

  9. MORE!

  10. Two Requirements of a Mechanism

  11. Two Requirements of a Mechanism

  12. Rate Determining Step The RATE DETERMINING STEP governs the rate law of the overall reaction.

  13. Mechanism must be consistentwith rate law

  14. Typical Problem- Try it!

  15. For the overall reaction, did you get?2NO2 + F2 --> 2 NO2F What is the INTERMEDIATE SPECIES? Ans. F What is the Rate Law? Rate = k [NO2][F2]

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