1. Chemical Reactions and Equations
Chapter 12 - Lesson 3
Energy Changes and Chemical Reactions

2. Why do chemical reactions always involve a change in energy?
What is the difference between an endothermic and an exothermic reaction?
What factors can affect the rate of a chemical reaction?
Essential Questions
Lesson 3

3. Big Ideas What is a chemical reaction?
Understanding Chemical Reactions
Chemical Equations
What is a chemical reaction?

4. Chemical Energy in Bonds
Chemical Bond- a lasting attraction between atoms ions or molecules that enables the formation of chemical compounds.
Energy is stored in the bonds of chemical compounds.
Atoms rearrange when chemical bonds between atoms break.
When the bond breaks the energy is released.
Potential energy is stored there because the bond has the potential to release a certain amount of energy.
Energy is stored in the bonds of chemical compounds.
Atoms rearrange when chemical bonds between atoms break.
When the bond breaks the energy is released.
Potential energy is stored there because the bond has the potential to release a certain amount of energy.

5. Endothermic Reactions - Energy absorbed
Chemical reactions that absorb thermal energy are Endothermic reactions. For an endothermic reaction to continue, energy must be constantly added.
Reactants+thermal energy products
In an endothermic reaction, more energy is required to break the bonds of the reactants than is released when the products form. Therefore, the overall reaction absorbs energy

6. Exothermic Reactions - Energy released
Exothermic Reaction - a chemical reaction that releases thermal energy
Reactants Products +thermal energy
More energy is released when products form Than is required to break the bonds in the reactants
From greek exo-, means ‘outside’ and therm, means ‘heat’.

7. Activation Energy
All reactions require energy to start the breaking of bonds. This energy is called activation energy.
Activation Energy-The minimum amount of energy needed to start a chemical reaction.
Different reactions have different activation energies.
Ex: Rusting iron have low activation energy. Wood requires the thermal energy of a flame to start burning.

8. Reaction Rates 3 types of reaction rates:
Increase concentration & pressure
Increase temperature
Increase surface areas
Reaction Rates

9. Surface Area
Surface area is the amount of exposed, outer area of a solid.
Increased surface area increases the reaction rate as displayed in our alka seltzer lab we did yesterday.

10. Temperature
The measure of the average kinetic energy of the particles in a material.
Imagine a crowded hallway. If everyone in the hallway was running, they would probably collide with each other more often and with more energy than everyone walking. This is also when particles are moving faster.
At higher temperatures, the average speed of particles is greater.
The speed reactions in two ways. The particles first collide more often. Secondly, collisions with more energy are more likely to break chemical bonds.

11. Concentration & Pressure
Increasing the concentration of one or more reactants increases collisions between particles.
In gases, an increase in pressure pushes gas particles closer together.
When particles are closer together, more collisions occur.
An example of concentration and pressure is of a crowded hallway than in an empty hallway, people probably collide more often
Empty Hall vs Crowded Hall

12. Catalysts
-a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.
-a substance that causes a chemical reaction to happen in a different way than it would happen without that catalyst
-Common types of catalysts include enzymes, acid-base catalysts, and heterogeneous catalysts. - Lowers the activation energy of reaction

13. Enzymes
-a substance produced by a living organism that acts as a catalyst to bring out a specific biochemical reaction.
You can’t see most enzymes. Enzymes are a type of catalyst.
Enzymes increase your digestion.

14. Inhibitors
Inhibitor-a substance that slows down or prevents a particular chemical reaction or other process, or that reduces the activity of a particular reactant, catalyst, or enzyme.
Recall that an enzyme is a molecule that speeds reactions in organisms. However, some organisms, such as bacteria, are harmful to humans. Some medicines contain molecules that attach to enzymes in bacteria. This keeps the enzymes from working properly. If the enzymes can’t work, the bacteria die and can no longer infect a human. The active ingredients in these medicines are called inhibitors.
Inhibitors are very important in the food industry. Preservatives in food are substances
That inhibit, or slow, food spoilage.

20. What is temperature? The measure of kinetic energy.
What is an example of a catalysts? -Zach
How can a reaction absorb energy to start but still be exothermic?
When you use something on something else to start the reaction.
Answer: Enzymes
When the concentration or pressure increases what happens?
The particles start to collide which causes a faster reaction rate.
Which type of chemical reaction has only one reactant?
A- decomposition
B- double replacement
C- single replacement
D- synthesis
Nicole Engelmeyer
Enzyme?-What do enzymes help in your body? Kegan
Question: What Chemical Reaction releases thermal energy?
Answer-Digestion
Answer: Exothermic reaction