1. Chapter 7
Chemical reactions

2. I. DESCRIBING REACTIONS
Section 7.1
I. DESCRIBING REACTIONS

3. a. CHEMICAL REACTIONS REACTANTS –substance that undergo change
PRODUCTS – new substances formed as a result of that change
2Na + Cl → NaCl
(Reactants) (Product)
Burning is an example of a
chemical reaction. When
charcoal burns, the carbon
reacts with the Oxygen in
the air to produce carbon
dioxide and heat .

4. 1. Using equations to represent reactions
Burning of charcoal
Carbon + oxygen → carbon dioxide
C + O2 → CO2
Chemical equation – representation of a chemical reaction in which the reactants and products are expressed as formulas

5. Antoine Lavoisier French chemist
2. Conservation of mass
The Law of conservation of mass states that mass is neither created or destroyed in a chemical reaction
Antoine Lavoisier French chemist

6. B. Types of reactions ( Starts section 7.2)
Main types of reactions:
Synthesis reactions
Decomposition reactions
Single displacement reactions
Double displacement reactions
Combustion reactions

7. 1. Synthesis reaction
a reaction of at least two substances that forms a new more complex compound
Ex. A + B → AB
Ex. 2Na + Cl2 → NaCl
Ex. photosynthesis

8. 2. Decomposition
A reaction in which one compound breaks into at least two compounds
Ex. AB → A + B
Ex. 2H2O → 2H2 + O2

9. 3. Single replacement
A reaction in which atoms of one element take the place of atoms of another element or in a compound
Ex. XA + B → BA + X
Ex. 3CuCl2 + 2Al → AlCl3 + 3 Cu

10. 4. Double replacement
A reaction in which a gas, a solid precipitate or a molecular compound is formed from the apparent exchange of ions between two compounds
Ex. AX + BY → AY + BX
Ex. Pb(NO3)2 + K2CrO4 → PbCrO4 + 2KNO3

11. 5. Combustion reactions A reaction in which a compound and oxygen burn
CH O2 → CO H2O

12. 6. Reactions as electrons transfers (ends section 7.2)
1. Electrons are transferred in redox reactions
Reduction/Oxidation (redox)- a reaction that occurs when electrons are transferred from one reaction to another
Substances that accept electrons are reduced
Those that give up electrons are oxidized

13. C. Balancing equations ( section 7.1)
Notes on the board

14. SECTION 7.3
III.
ENERGY CHANGES IN REACTIONS

15. a. Chemical bonds and energy
Chemical energy is energy stored in chemical bonds of a substance
Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in products

16. a. Chemical bonds and energy (cont)
1. Breaking bonds
Breaking chemical bonds require energy
Why have no smoking signs at gas stations?
Isotane molecule and oxygen react, BUT they need energy to get started.
Bonds have to be broken for energy to be released (heat, electricity, light)

17. B. Exothermic and endothermic reactions
2. Endothermic Reactions – Transfers energy to the reactants
1.Exothermic Reactions- Transfers energy from the reactants to the surroundings

18. Section 7.4
IV. REACTION RATES

19. A. Factors affecting reaction rates
1. Temperature
2. Surface Area
Increasing the temperature of a substance causes the particles to move faster to speed up a reaction.
An increase in surface area increases the exposure of reactants to one another
Ex. Which medicine would work faster a pill or BC powder?

20. A. Factors affecting reaction rates(cont)
3. Stirring
4. Concentration
Increase exposure of reactants to each other by stirring them
Ex. Washing clothes
The reacting particles present in a given volume, the more opportunities there are for collisions involving those particles

21. A. Factors affecting reaction rates
5. Catalysts – substance that affects the reaction rate without being used up
Speed up reactions

22. Section 7.5
V. Equilibrium

23. A. Types of equilibrium
1. Physical Equilibrium
2. Chemical Equilibrium
When a physical change does not go to completion , a physical equilibrium is established between the forward and reverse changes
When a chemical reaction does not go to completion, a chemical equilibrium is established between the forward and reverse reactions

24. B. Factors Affecting chemical equilibrium
1. Temperature
2. Pressure
3. Concentration

25. The End