1. Section 3 – pg 234 Controlling Chemical Reactions
Chapter 6
Section 3 – pg 234
Controlling Chemical Reactions

2. Activation Energy Pg 235 Chemical reactions require energy to start
The energy is used to break the chemical bonds of the reactants
The atoms then begin to form the new chemical bonds of the products
Activation Energy: the minimum amount of energy needed to start a chemical reaction

3. Exothermic and Endothermic Reactions
Every chemical reaction needs activation energy to get started
Whether or not a reaction needs still more energy from the environment is dependant on if the reaction is exothermic or endothermic
Exothermic Reaction Endothermic Reaction
Heat released Heat Absorbed
Pg 236

4. The products have less energy than the reactants
Pg 236
The products have less energy than the reactants
Due to release of energy (heat) to surroundings
IE: burning of fuel
Activation Energy
Heat Released

5. Pg 236
Endothermic reactions need activation energy to get started and needs energy to keep going
The energy of the products is higher than that of the reactants due to heat absorption
Activation Energy
Heat Absorbed

6. Rates of Chemical Reactions
Pg 237
Rates of Chemical Reactions
Chemical reactions do not occur at the same rates
Some are fast – like in explosions
Some are slow – like the formation of rust
Factors that affect rates of reaction include surface area, temperature, concentration, and the presence of catalysts or inhibitors

7. Pg 237
Surface Area
During a reaction between a solid and a liquid or gas, only the particles on the surface of the solid come in contact with the other reactants
If the solid is broken down into smaller pieces, there is more surface area (more particles are exposed), and the reaction will happen faster

8. Pg 238
Temperature
Increased temperature increases the rate of reaction
Particles move faster causing them to interact more
The faster moving particles have more energy providing the reaction with its activation energy
Reducing Temperature slows down rates
This is why we refrigerate food (slow down the multiplication of bacteria)

9. Pg 238
Concentration
Concentration: the amount of a substance in a given volume
Increasing the concentration of reactants supplies more particles to react

10. Pg 239
Catalysts
Another way to control rate of a reaction is to change the activation energy needed
Catalyst: a material that increases the rate of a reaction by lowering the activation energy
The catalyst is not changed by the reaction so it is not considered a reactant

11. Pg 239
Most chemical reactions happens at a high enough temperature to kill living things
Our bodies contain biological catalysts that lower this temperature so we don’t die (yay!)
Enzyme: biological catalyst; each one is specific to a single type of reaction

12. Pg 239
Inhibitors
Inhibitor: a material used to decrease the rate of a reaction
Prevent reactants from coming together by combining with one of the reactants either permanently or temporarily

13. Chapter 6 Section 3 Homework – pg 239

14. 1A. What is activation energy?

15. 1B. What role does activation energy play in chemical reactions?

16. 1C. Look at the diagram in figure 13, and make a generalization about activation energy in exothermic and endothermic reactions

17. 2A. What are four ways that chemists can control the rates of chemical reaction?

18. 2B. Which would react more quickly in a chemical reaction: a single sugar cube or an equal mass of graduated sugar crystals? Explain.