Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.
-
Upload
ethan-williams -
Category
Documents
-
view
231 -
download
0
Transcript of Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.
![Page 1: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/1.jpg)
Reaction Rates
Chapter 17
Honors Chemistry
![Page 2: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/2.jpg)
Red Blue
Reaction Rates
![Page 3: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/3.jpg)
Reactions can be…
FAST!
Liquid hydrogen and oxygen reacting to launch a shuttle
![Page 4: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/4.jpg)
..or
S
L
O
WConcrete hardening
![Page 5: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/5.jpg)
..or
S
L
O
W
Watching paint dry
![Page 6: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/6.jpg)
Expressing rxn rates in quantitative terms
quantityAverage rate
t
![Page 7: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/7.jpg)
Example: Reaction data for the reaction between butyl chloride (C4H9Cl) and water is given below. Calculate the average reaction rate over this time period expressed as moles of C4H9Cl consumed per liter per second.
quantityAverage rate
t
[C4H9Cl] at t=0.00 s
[C4H9Cl] at t=4.00 s
0.220 M 0.100 M
mol molL L(0.100 - 0.220 )
(4.00 s - 0.00 s)
Table 17-1: Molar Concentration
initialfinal
initial94final94
tt
Cl]H[C - Cl]H[C
molL-0.120
4.00 s
molL s -0.0300
![Page 8: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/8.jpg)
Collision Theory Atoms, ions and molecules must
collide in order to react. Reacting substances must collide with
the correct orientation. Reacting substances must collide with
sufficient energy to form the activated complex.
![Page 9: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/9.jpg)
Orientation and the activated complex
Analogy: if you start with two separate paperclips (reactants) and you wish to link them together (products), not only must the paperclips come into contact, but they also must collide with a specific orientation.
![Page 10: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/10.jpg)
Orientation and the activated complex
Biological example: ENZYMES
You’ll learn much more about this next year
![Page 11: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/11.jpg)
Activation energy and reaction
Only collisions with enough energy to react form products
![Page 12: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/12.jpg)
Activation energy and reaction
![Page 13: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/13.jpg)
Activation energy and reaction
Another example
Activated complex (also called transition state)
reactants
products
![Page 14: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/14.jpg)
Does ∆G tell us anything about rxn rate?
NO If a reaction is spontaneous, it does not
follow that it is fast or slow. Thus, a new branch of chemistry…
kinetics
![Page 15: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/15.jpg)
Factors affecting reaction rates
1) The nature of the reactants
2) Concentration
3) Pressure (gases only)
4) Surface area
5) Temperature
6) Catalysts
![Page 16: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/16.jpg)
NATURE OF REACTANTS
Some elements/compounds are more reactive than others
sodium in water (alkali metals are VERY reactive)
FAST
![Page 17: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/17.jpg)
NATURE OF REACTANTS
Some elements/compounds are more reactive than others
Rusting of iron (it takes time for moisture in the air to oxidize the metal… process can be sped up if salt is present, but will still not react as fast as sodium and water)
SLOW
![Page 18: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/18.jpg)
CONCENTRATION
As concentration ↑, frequency of collisions ↑, and therefore rxn rate ↑
![Page 19: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/19.jpg)
PRESSURE (gases)
For gases, increasing pressure creates the same effect as increasing concentration
![Page 20: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/20.jpg)
SURFACE AREA
← slow
fast
As surface area ↑, rxn rate ↑
![Page 21: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/21.jpg)
TEMPERATURE:
Generally, ↑ temp = ↑ rate Why? Higher temp = faster molecular motion
= more collisions and more energy per collision = faster rxn
Analogy: imagine that you are baby-sitting a bunch of 6 year olds. You put them in a yard and you let them run around. Every now and then a couple of kids will run into each other. Now imagine that you decide to feed them some sugar. What happens? They run around faster and of course there are many more collisions. Not only that, the collisions are likely to be a lot harder/more intense.
![Page 22: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/22.jpg)
CATALYST
Provides an easier way to react
Lowers the activation energy
Enzyme = biological catalyst
Catalyst: a substance that speeds up the rate of a reaction without being consumed in the reaction.
![Page 23: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/23.jpg)
CATALYST
Adding a catalyst speeds up the rxn by lowering the activation energy
![Page 24: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/24.jpg)
Reaction Rate Laws
The equation that expresses the mathematical relationship between the rate of a chemical reaction and the concentration of reactants is a rate law.
k[A]Rate
BA :reaction the For
*where k is a constant specific to this reaction
![Page 25: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/25.jpg)
Reaction Order
The reaction order for a reactant defines how the rate is affected by the concentration of that reactant.
The overall reaction order of a chemical reaction is the sum of the orders for the individual reactants in the rate law.
![Page 26: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/26.jpg)
Reaction Order
The rate law for most reactions has the general form….
Rate = k[reactant 1]m[reactant 2]n… The exponents m and n are called
reaction orders. Their sum (m + n) is called the overall reaction order.
![Page 27: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/27.jpg)
Reaction Order For the reaction aA + bB products
Rate = k[A]m[B]n
where m and n are the reaction orders for A and B respectively
Only if the rxn between A and B happens in a single step (with a single activated complex… which is unlikely) does m=a and n=b.
Thus, the values of m and n must be determined experimentally!!!
![Page 28: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/28.jpg)
Reaction Order
For the reaction aA + bB products
Rate = k[A]m[B]n
where m and n are the reaction orders for A and B respectively
Rate laws cannot be predicted by looking at a balanced chemical equation.
![Page 29: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/29.jpg)
Finding the rate law
The most common method for experimentally determining the differential rate law is the method of initial rates.
In this method several experiments are run at different initial concentrations and the instantaneous rates are determined for each at the same value of time (as near t = 0 as possible)
![Page 30: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/30.jpg)
Using Initial Rates to Determine the Form of the Rate Law
Exp # [A] [B] Initial Rate (M/s)
1 .100M .100M 4x10-5
2 .100M .200M 4x10-5
3 .200M .100M 16x10-5
A + B C
From this data, find the form of the rate law..
Rate = k[A]m[B]n
![Page 31: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/31.jpg)
Exp # [A] [B] Initial Rate (M/s)
1 .100M .100M 4x10-5
2 .100M .200M 4x10-5
3 .200M .100M 16x10-5
5
5
2 4 10 [.100] [.200]1 4 10 [.100] [.100]
m n
m n
Rate kRate k
[.200]1
[.100]
n
n
1 2n
n = 0
Rate = k[A]m[B]n
![Page 32: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/32.jpg)
Exp # [A] [B] Initial Rate (M/s)
1 .100M .100M 4x10-5
2 .100M .200M 4x10-5
3 .200M .100M 16x10-5
Rate = k[A]m[B]n
5
5
3 16 10 [.200] [.100]1 4 10 [.100] [.100]
m n
m n
Rate kRate k
[.200]4
[.100]
m
m
4 2m
m = 2
![Page 33: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/33.jpg)
Exp # [A] [B] Initial Rate (M/s)
1 .100M .100M 4x10-5
2 .100M .200M 4x10-5
3 .200M .100M 16x10-5
Rate = k[A]m[B]n
Rate = k[A]2[B]0
Rate = k [A]2
![Page 34: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/34.jpg)
Exp # [A] [B] Initial Rate (M/s)
1 .100M .100M 4x10-5
2 .100M .200M 4x10-5
3 .200M .100M 16x10-5
2 0[ ] [ ]rate
kA B
5
32
4 104 10
[.100]
Rate = 4x10-3 [A]2
Now, solve for k… Rate = k [A]2
![Page 35: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/35.jpg)
Knowing rate laws and rate orders helps us predict how the reaction will proceed over time
Application: Radioactive decay
is a first order reaction
Half life is constant over time
Allows us to date fossils, etc.
![Page 36: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/36.jpg)
Reaction Mechanisms Most chemical reactions consist of a
sequence of two or more steps (or simpler reactions). These add together to create the overall reaction equation.
Generally, some steps will be fast and others will be slow.
The slow step is the rate determining step.
![Page 37: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/37.jpg)
The reaction between NO2 and CO has the overall reaction:
NO2 + CO NO + CO2
A study of the kinetics of this reaction revealed the rate law for the reaction is.
Rate = k[NO2]2
This Rate Law requires that the slow step of the reaction involves a collision between two NO2 molecules. How can this be a step in the seemingly simple reaction above?
Example:
![Page 38: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/38.jpg)
NO2 + CO NO + CO2
NO2 + NO2 NO3 + NO
NO3 + CO NO2 + CO2
2NO2 + NO3 + CO NO2 + NO3 + NO + CO2
NO2 + CO NO + CO2
Further study of this reaction established that two NO2 molecules can react as follows…
NO3 is a highly reactive material which is capable of transferring an oxygen atom.
![Page 39: Reaction Rates Chapter 17 Honors Chemistry Red Blue Reaction Rates.](https://reader034.fdocuments.net/reader034/viewer/2022050909/5697bfd71a28abf838cae868/html5/thumbnails/39.jpg)
NO2 + CO NO + CO2
NO2 + NO2 NO3 + NO
NO3 + CO NO2 + CO2
NO2 + CO NO + CO2
slow
fast
The first equations sets the rate law, so it must be the slow one.
Remember, the rate law only provides information about the slowest reaction in the mechanism.