1. CHEMICAL REACTIONS
UNIT 5

2. Evidence of Chemical Reactions
Heat or light
Color change
Odor change
Release of gas (bubbles)
Formation of a solid (precipitate)

3. Law of Conservation of Matter
Matter is neither created nor destroyed in ordinary chemical reactions
Must have equal numbers of atoms on both sides of the equation to obey this Law.

4. Chemical Equations X + Y  XY Coefficients
Statements using words or formulas that describes a chemical change.
Consists of two parts
Reactants
Starting substances in a chemical change
Always written on the left side of an equation
Products
Substances formed in a chemical reaction
Always written on the right side of the equation
Coefficients
Numbers in front of formulas used to balance the numbers of atoms in an equation
X + Y  XY
reactants
products

5. Diatomic Elements
7 elements that are formed by bonding two atoms of that element.
Are written as diatomic molecules in the elemental form
Br, I, N, Cl, H, O, & F
Ex: Bromine = Br2
Mr. “BrINClHOF

6. Examples H2 + Br2  HBr Mg + NaOH  Mg(OH)2 + Na
hydrogen + nitrogen  ammonia
Sulfur + oxygen  sulfur trioxide

7. Types of Reactions

8. Types of Reaction X + Y  XY XY  X + Y
Synthesis: 2 or more substances combine into 1
Decomposition: 1 substance breaks down into2 or more simpler ones
X + Y  XY
XY 
X + Y

9. Types of Reaction XY + Z  XZ + Y XY + AB  XB + AY
Single replacement: one element replaces another in a compound
Double replacement: two compounds form 2 new ones
XY + Z 
XZ + Y
XY + AB 
XB + AY

10. Types of Reaction CH4 + 2O2  CO2 + 2H2O HCl + NaOH  NaCl + H2O
Combustion: carbon compound burns in oxygen to form carbon dioxide and water.
Acid-Base: an acid & base react to form a salt & water.
CH4 + 2O2 
CO2 + 2H2O
HCl + NaOH 
NaCl + H2O

11. Practice ammonia  hydrogen & nitrogen
magnesium + oxygen  magnesium oxide
hydrochloric acid + calcium hydroxide calcium chloride + water
zinc + hydrobromic acid  zinc bromide + hydrogen
magnesium oxide + calcium fluoride  magnesium fluoride + calcium oxide
methane (CH4) + oxygen  carbon dioxide + water