1. Chapter Highlights and Notes
Holt Chapter 15
Chapter Highlights and Notes

2. Section 1
Chemical reactions form new substances with different properties than the starting substances
Properties such as presence of a gas, temperature change, color change, precipitate appears, odor develops, solid disappears, etc.

3. Clues that a chemical reaction is taking place include:
- formation of a gas (often CO2)
- formation of a solid
- a color change
- and energy change (heat produced -> hotter - or- heat removed -> colder)

4. A chemical formula tells the composition of a compound using chemical symbols and subscripts.
Subscripts are small numbers to the right of a symbol in a formula.
H2O (the 2 is a subscript)
2 atoms of H, 1 atom of O

5. Chemical formulas can sometimes be written from the names of covalent compounds and ionic compounds.

6. A chemical equation describes a reaction using formulas, symbols, and coefficients.

7. A balanced equation uses coefficients to illustrates the law of conservation of mass, that mass is neither created nor destroyed during a chemical reaction.
The 2 in 2NaCl is the coefficient (there are 2 atoms of Na and 2 atoms of Cl)

8. Section 2
Many chemical reactions can be classified as one of four types by comparing reactants with products.
Synthesis
Single replacement
Double replacement
Decomposition

9. Synthesis reactions
- the reactants form a single product
2H2 + O2 --> 2H2O

10. Single Replacement reactions
A more-reactive element takes the place of a less-reactive element in a compound.
Zn + 2HCl --> ZnCl2 + H2

11. Decomposition Reactions
A single reactant breaks apart into two or more simpler products
H2CO3 --> H2O + CO2

12. Double Replacement reaction
Ions in two compounds switch places.
A gas or precipitate is often formed
NaCl + AgNO3 --> NaNO3 + AgCl

13. Section 3 Energy is released in exothermic reactions.
The energy released can be written as a product in a chemical equation

14. Energy is absorbed in endothermic reactions.
The energy absorbed can be written as a reactant in a chemical equation.

15. The law of conservation of energy states that energy is neither created nor destroyed.

16. Activation energy is the energy needed to start a chemical reaction.

17. Energy diagrams indicate:
Exothermic - energy is given off
Endothermic - energy is absorbed

18. The rate of a chemical reaction is affected by:
- temperature
- concentration
- surface area
- presence of catalyst
- presence of inhibitor

19. To increase the rate of reaction:
- Increase temperature and/or
- increase concentration and/or
- increase surface area and/or
- add a catalyst

20. The end