1. Chapter 1: Chemical Reactions

2. Section 1: Forming New Substances
Chemical Changes are responsible for leaf coloring
Chemical Reactions
Process of one or more substance undergoes change to produce one or more different substances
New substances had different chemical and/or physical characheristics

3. Clues to Chemical Reactions
Gas Formation
Solid Formation (Precipitate)
Color Change
Energy Change
Breaking and Making Bonds
New Substance Formed because: bonds break, atoms are rearranged, and new bonds form

4. Chemical Formulas Chemical Symbol-short-hand for identifying elements
Chemical Formula-short-hand notation for a compound or diatomic element
H2O
2 indicates 2 hydrogen
Subscript—smaller/lower number
No subscript indicates 1 atom of the element

5. Examples:
O2 2 Oxygen atoms
C6H12O6 6 Carbon, 12 Hydrogen, Oxygen

6. Writing Formulas for Covalent Compounds
Usually made from two nonmetals
Name can help write the formula
Prefix often tells the # of atoms
Mono-1 Hexa-6
Di-2 Hepta-7
Tri-3 Octa-8
Tetra-4 Nona-9
Penta-5 Deca-10

7. Writing Formulas for Ionic Compounds
Likely to contain name of metal and nonmetal
Overall charge must be zero—must balance with subscripts
NaCl MgCl2

8. Chemical Equations
Shorthand description of a chemical reaction using chemical symbols
Understood throughout the world—no translation needed

9. Reactants Yield Products
Reactants—starting materials of a reaction
Products—substances formed from the reaction
C O CO2
Reactants Products
Separate elements with (+)
Arrow reads as “yields”

10. Accuracy is important Diatomic elements: H2, N2, O2, Fl2, Cl2, Br2 ,I2
Inaccuracies can misrepresent information/characteristics
CO2—carbon dioxide/harmless gas
CO—carbon monoxide/poisonous gas
Co—Cobalt/grey metal

11. An Equation Must Be Balanced
Atoms are not gained or lost in a reaction
Number of reactant atoms must equal the number of product atoms

12. How to Balance an Equation
Coefficients: number in front of a chemical symbol/formula
To find the number of atoms:
Multiply the coefficient by the subscript
2CO2 2 Carbon, 4 Oxygen

13. Steps to Balancing Count the atoms on each side of the equation
Balance by adding coefficients
Recount and Repeat as Needed
H2 + O H2O
H = 2 H = 2 UNBALANCED
O =2 O= 1
H2 + O H2O
H = 2 H = 4 UNBALANCED
O =2 O= 2
2H2 + O H2O
H = 4 H = 4 BALANCED

14. Mass Is Conserved—It’s A Law!
Law of Conservation of Mass: mass is neither created nor destroyed in an ordinary chemical or physical change
Same number of each type of atom are found on each side of the equation

15. Section 2: Types of Chemical Reactions
4 Categories of Reactions: Synthesis, Decomposition, Single-Replacement, and Double Replacement Reactions

16. Synthesis Reactions
Two or more substances combine to form a single substance
2 Na Cl NaCl

17. Decomposition Reaction
Single compound breaks down to form two or more simple substances
Reverse of synthesis reaction
H2CO H2O CO2

18. Single-Replacement Reaction
One element takes the place of another element in a reaction
Some elements are more reactive than others
More reactive elements replace less reactive elements
2N HCl NCl H2

19. Double-Replacement Reactions
Ions in two compounds switch position
Often a gas or precipitate is formed
NaCl + AgF NaF + AgCl

20. Section 3: Energy and Rate of Chemical Reactions
Every Reaction Involves Energy
Bonds break with absorbed energy
Bonds form with energy release
Energy is Released in Exothermic Reactions
Energy removed as light, electrical, or heat
Energy is Absorbed in Endothermic Reactions
Energy added—listed on left of equation

21. Section 3: Energy and Rate of Chemical Reactions
Energy is Conserved—It’s a Law!
Energy is neither created nor destroyed
Activation Energy Gets a Reaction Started
Activation Energy: minimum amount of energy needed for a substance to react
Exothermic—energy released as a product supplies the activation energy to continue the reaction
Endothermic—energy is needed to be supplied to keep the reaction going

22. Factors Affecting Rates of Reactions
Rates of Reactions—How rapidly the reaction takes place
Temperature
Concentration
Surface Area
Presence of Catalyst or Inhibitor

23. Temperature
Increase temperature increases rate
Particles move faster and collide
Concentration
Concentration: Amount of substance dissolved in another
Greater concentration generally increases the rate
More substances are closer together and collide

24. Surface Area
Increasing Area Speeds Rate
Grinding particles to powder exposes more of reactants and more collide
Catalysts and Inhibitors
Catalysts: substances that speed up reactions without permanently being changed
Inhibitor: substance that slows down or stops a chemical reaction