Chemistry 2.2

ChemistryChapter 2 - Section 2

Rates of Chemical Reactions

Tuesday, July 10, 2012

How Fast?


Some reactions need some help to get started,

others do not.


“What is that extra help

called?”


Activation Energy


The minimum amount

of energy needed to start a reaction.


Let’s look at an example:

2O2 + CH4 --> CO2 + 2H2O



Activation Energy

9


Activation Energy

9

For a reaction to begin, the molecules must bump into each other or collide with enough force.


Activation Energy

9


The reactants must smash into each other with a certain amount of energy. If they do not, the reaction will not occur.


Activation Energy

9



This energy is called, activation energy.


Activation Energy

9



This energy is called, activation energy.

This is also true for reactions that release energy when they react. An example is gasoline burning.


When gasoline is spilled it does not burst into flames.


A highly flammable material, which cannot be extinguished by wind or rain

needs to be lit in order to burn. Tuesday, July 10, 2012

Rate of Reaction?


How fast a reaction occurs after it has

started.


You can measure Reaction Rate by:

- how quickly one of the reactants is consumed,

or- how quickly one of the

products is created


Rate of Reaction - The faster the better


Rate of Reaction - Fast is not good here


What controls reaction rate?

1. temperature2. concentration 3. surface area

4. inhibitors


Temperature Changes Rate





Slow the ripening of fruit by putting them in the refrigerator.




Meat and fish decompose faster at higher temperatures, producing toxins that can make you sick. Keep them chilled helps slow the decomposition rate.




Meat and fish decompose faster at higher temperatures, producing toxins that can make you sick. Keep them chilled helps slow the decomposition rate.

Bacteria grow faster at higher temperature.


Temperature Affects Rate





Most chemical reaction speed up when temperature increase.




The atoms and molecules are always moving, and they move faster at higher temperatures.




The atoms and molecules are always moving, and they move faster at higher temperatures.

Faster molecules collide with each other more often and with greater force, which may be enough to break the old bond. This is activation energy.


Concentration Affects Rate


Concentration?


Amount of substance in a certain volume.


Surface Area Affects Rate

10 cm 10 cm

10 cm



10 cm

Surface Area = 600 cm2

10 cm

10 cm



10 cm

Surface Area = 600 cm2

That is the amount of

surface that would be

touching the other

reactant.

10 cm

10 cm


10 cm

What if we cut out little cubes? 1cm x 1cm


10 cm

10 cm

1 cm 1 cm


10 cm


How many cubes would we have?


10 cm

10 cm

1 cm 1 cm


10 cm



1000 cubes


10 cm

10 cm

1 cm 1 cm


10 cm



1000 cubes

What would be the SA of one of the cubes?


10 cm

10 cm

1 cm 1 cm


10 cm



1000 cubes

What would be the SA of one of the cubes?

6cm2


10 cm

10 cm

1 cm 1 cm


10 cm

What is the total SA of all the cubes?


10 cm

10 cm


10 cm


6cm2 x 1000 =


10 cm

10 cm


10 cm


6cm2 x 1000 =

6000 cm2


10 cm

10 cm


10 cm


6cm2 x 1000 =

6000 cm2

SA of Whole cube = 600 cm2

SA of cut up cube = 6000 cm2


10 cm

10 cm


10 cm That’s a

BIG difference!



10 cm That’s a

BIG difference!

SA of Whole cube = 600 cm2

SA of cut up cube = 6000 cm2



Slowing Down

Reactions


Inhibitor?


A substance that slows down a chemical reaction. An inhibitor

makes the formation of a certain amount of product take

longer.


Inhibitor

Butylated hydroxytoluene (BHT)


Speed Up Reactions


Catalyst?


A substance that speeds up a chemical reaction.

Catalyst’s do not appear in a chemical equation

because they are not changed permanently or

used up.


Catalysts - provide a surface for

the reaction to take place,

or - reduce the activation energy needed to start

the reaction


37


Catalytic Converter


Catalytic Converter


Catalytic Converter

In vehicles, the exhaust passes through the catalyst.


Catalytic Converter


Catalysts will speed up the reactions that change incompletely burned substances that are harmful, such as carbon monoxide, into less harmful substances like CO2 and H2O.


Catalytic Converter


Catalysts will speed up the reactions that change incompletely burned substances that are harmful, such as carbon monoxide, into less harmful substances like CO2 and H2O.

This results in cleaner air. Tuesday, July 10, 2012

Catalytic Converter


Catalytic Converter


Enzymes are Specialists!


Enzyme?


Large protein molecules that speed up reactions needed for

your cells to work properly.

- convert food to fuel- build bone and muscle tissue- convert extra energy to fat

- produce other enzymes



Other Uses of Enzymes

One example is Proteases - a class of enzymes that work within cells to break down proteins.

Meat tenderizer is one example of a protease.

Contact lens cleaning solutions also contain

proteases that break down proteins formed by your eyes that can collect on your lenses and

cloud your view.


Finished the KNP!

So, lets see a catalyst at

work!


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Chemistry 2.2

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