1. Controlling Chemical Reactions
Chapter 6section 3
Mr. Sapalicio
Monterey Highlands Elementary School
Chemistry and Physical Science

2. Activation energy
Activation energy- The minimum amount of energy needed to start a chemical reaction.
All chemical reactions require a certain amount of energy to get started.
Example- hydrogen and oxygen are two gases. They can be together for a long time and never react. Once a small spark combines just a few molecules the release of energy can trigger the other molecules to react.
What is required for oxygen and hydrogen to react?
Activation energy

3. Exothermic Reactions
Exothermic reactions- Middle line is energy before the reaction.
The peak of the graph represents the activation energy.
Notice at the end of the graph the products
have less energy than the reactants.
This results from a release in heat

4. Endothermic Reactions
Endothermic reactions- Reactants lower than products because it will require an absorption of energy.
The peak of the graph represents the activation energy.
Notice at the end of the graph the products
have more energy than the reactants.
This results from an absorption in heat.
They also require energy to keep going.

5. Rates of chemical reactions
Factors that affect rates of reaction include;
SURFACE AREA
TEMPERATURE
CONCENTRATION
PRESENCE OF CATALYSTS, or INHIBITORS.
To speed up a chemical reaction you must increase the amount of reactant particles and more energy.

6. Surface area
Surface area- The more surface a particle has the faster it can break down.
Ex: chewing food easier to break down when
there is more surface area.
It is the breaking down of a particle to
Increase its ability to break down.

7. Temperature
Increasing the heat increases the movement of the particles.
In doing so, the particles are more likely to come into contact which means there is more of a chance of a reaction going to take place.
Also, the higher energy allows for the particles to be closer to going over the activation energy “hill”
ex: in milk there is bacteria which carry out thousands of small chemical reactions, at room temperature they will react faster, so it is a lot better to leave the milk in the fridge.
The cooler the temperature the slower the reactions.
The hotter the temperature the faster the reactions.

8. Concentration
Concentration- the amount of a substance in a given volume.
“adding a lot of sugar to a glass of water will make the drink concentrated with sugar.”
Increasing the concentration of reactants makes it more likely that particles will react.

9. ?
Why may an increase in temperature affect the rate of chemical reaction?
It will allow particles to have more energy to come into contact with each other and reach the activation energy level.

10. Catalysts
Catalyst- a material that increases the rate of reaction by lowering the activation energy.
Catalysts are not reactants. They only bring the reactants closer together to enhance the reaction.
An Enzyme is an example of a catalyst that is in your body.
Enzyme- cell in the body that contain biological catalysts.
We need enzymes because it would take toooo much energy for all of our bodies chemical reactions.

11. Catalysts

12. Inhibitors A material used to slow down the rate of reaction.
This helps in the process of preserving food keeping them from stale or spoiled.
“Preservatives added”