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YouTube Video: http://www.youtube.com/watch?v=D7TfmT85Cjw

http://www.youtube.com/watch?v=rl50M­wNVcsNOTES:

Reaction Pathway Diagrams

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Lower PE means....       Molecules are more stable       The molecules have higher KE

Higher PE means....       Molecules are less stable       The molecules have lower KE

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What happens during a chemical reaction?

A + B2 AB + B

A

B2

Assume that both reactants are moving with enough speed that upon colliding with each other, a reaction will occur (the molecules have the required energy necessary to cause a reaction, known as the activation energy). 

Draw a diagram of the activated complex. What happens to the speed of the molecules at this point? Why? 

Draw a diagram of the products. What happens to the speed of the molecules at this point? Why? 

Potential energy increases from beaker one to beaker two since the possibility of a reaction occuring is increasing

Potential energy decreases from beaker two to beaker three since there is less of a chance of a reaction.

What is happening to the kinetic energy of the molecules from beaker one to beaker two?

What is happening to the kinetic energy of the molecules from beaker two to beaker three?

SUMMARY: As _______ energy increases, ______ energy decreases 

(AND VICE VERSA!!)

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What happens during a chemical reaction?

A3 + B2 A2B + AB

Assume that both reactants are moving with enough speed that upon colliding with each other, a reaction will occur (the molecules have the required energy necessary to cause a reaction, known as the activation energy). 

Draw a diagram of the activated complex. What happens to the speed of the molecules at this point? Why? 

Draw a diagram of the products. What happens to the speed of the molecules at this point? Why? 

Potential energy increases from beaker one to beaker two since the possibility of a reaction occuring is increasing

Potential energy decreases from beaker two to beaker three since there is less of a chance of a reaction.

What is happening to the kinetic energy of the molecules from beaker one to beaker two?

What is happening to the kinetic energy of the molecules from beaker two to beaker three?

SUMMARY: As _______ energy increases, ______ energy decreases 

(AND VICE VERSA!!)

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What do you notice about these graphs?What information is provided by these graphs?

SUMMARY:

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PROBLEM SET #1

Reaction Progress

Potential Energy(kJ)

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Recall: A reaction mechanism is a series of steps that lead to a desired overall reaction.

The rate of an entire mechanism is determined by the slowest step in the mechanism. Therefore,the slowest step of a reaction mechanism is called the rate determining step.

Consider a relay race in which a turtle and superman are on the same team. 

2. 1. 

Step 1: Vancouver to ReginaStep 2: Regina to Winnipeg

ANALOGY:

(a) Explain how long the "relay reaction" will take if the turtle is running leg 1 of the relay.

(b) Explain how long the "relay reaction" will take if Superman is running leg 1 of the relay.

YouTube: http://www.youtube.com/watch?v=eGaec7V1U28

In small groups, take notes as you watch the video. What did you learn?

Problem: 

Step (1) NO2 + NO2 à NO3 + NOStep (2) NO3 + CO à NO2 + CO2

     What happens in the mechanism given above if the first step       is rate determining? Explain in terms of the production and       consumption of the reaction intermediate(s). [What happens       if the first step speeds up? Slows down? What is the general       speed of the second step]

What happens in the mechanism if the second step is rate determining? 

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Problem: 

Step (1) NO2 + NO2 à NO3 + NOStep (2) NO3 + CO à NO2 + CO2

     What happens in the mechanism given above if the first step       is rate determining? Explain in terms of the production and       consumption of the reaction intermediate(s). [What happens       if the first step speeds up? Slows down? What is the general       speed of the second step]

What happens in the mechanism if the second step is rate determining? 

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MAIN IDEAS: A catalyst is something that “looks” to be unchanged in a chemical reaction. Its purpose it to create a new pathway for a reaction that lowers the activation energy of the process, allowing for a faster reaction. You can identify a catalyst in two ways: 1) The reactant that also occurs as a product (unchanged) if a single step reaction will likely be a catalyst for the reaction. 

OR….2) In a multi­step reaction mechanism, any reactant that is used up in an early step, but is reproduced in a later step will likely be a catalyst for the mechanism.

A reaction intermediate occurs only in multi­step reaction mechanisms ­ and you can identify reaction intermediates by finding a compound/substance that is formed (is a product) of an early step, but is used up (becomes a reactant) in a later step ­ and therefore, a reaction intermediate will NOT show up in an overall reaction equation!

When drawing reaction pathway diagrams for catalyzed reactions:

à The catalyzed reaction must have a lower activation energy than the uncatalyzed reaction. 

à If the catalyzed reaction occurs as a multi­step reaction mechanism, the number of “bumps” in the reaction pathway     graph is equal to the number of steps occurring in the reaction mechanism. 

à RECALL ­ For an exothermic reaction, the reactants will be high energy  (higher on the graph) than the products     (which will be low energy) AND for endothermic reaction, the reactants will be lower energy (lower on the graph) than     the products (which will be higher on the graph).  

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ASSIGNMENT