1. (NH4)2Cr2O7 (s)  N2(g) + Cr2O3 (s) + 4H2O(g)
9.1 Chemical Equations
Represents, w/ symbols & formulas, the reactants & products in a chemical reaction
Requirements
Must represent the known facts
Must contain correct formulas
Must satisfy the law of conservation
(NH4)2Cr2O7 (s)  N2(g) + Cr2O3 (s) + 4H2O(g)

2. Word & Formula Equations
Word Equation – chemical equation represented w/ words
Methane Gas + Oxygen Gas  Carbon Dioxide Gas + Water Vapor
Formula Equation – chemical equation represented w/ formulas & symbols
CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O (g)
Coefficient
Small whole number used to balance the equation

3. Common Symbols in Equations
Explanation 
“Yields” indicates result of reaction 
Reversible Reaction
(s)
Reactant or Product in solid state 
Precipitate (alternative for solid)
(l)
Reactant or Product in liquid state
(aq)
Reactant or Product in aqueous solution (dissolved in water)
(g)
Reactant or Product in gas 
Gaseous Product (alternative for gas)
Reactants are Heated

4.  NaOH + HNO3 NaNO3 + H2O Practice 
Solid Sodium hydroxide reacts with nitric acid in a solution to produce sodium nitrate and water when heated.
Write a word and formula equation for this sentence.
Sodium Hydroxide + Nitric Acid  Sodium Nitrate + Water  
NaOH +
HNO3
NaNO3 +
H2O
(s)
(aq)
(aq)
(l)

5. 2nd Practice Equation
Aluminum sulfate and calcium hydroxide are used in a water purification process. When added to water they dissolve and react to produce two insoluble (solid) products, aluminum hydroxide and calcium sulfate. Write a word and formula equation representing this reaction.
Aluminum Sulfate + Calcium Hydroxide  Aluminum Hydroxide + Calcium Sulfate
Al2(SO4)3 (aq) + Ca(OH)2 (aq)  Al(OH)3 (s) + CaSO4 (s)

6. Indication of a Chemical Reaction
Production of light or heat.
Production of gas or smoke.
Formation of a precipitate (ppt).
Color change.

7. Oscillating Reaction

8. Silver Reactions

9. Thermite Reaction

10. Balancing Equations Mass of Reactants must equal Mass of Products
No Atoms can be lost during the reaction

11. 9.3 Types of Chemical Equations
Synthesis (Combination)
A + X  AX
Decomposition
AX  A + X
Single Replacement
A + BX  AX + B
Double Replacement
AX + BY  AY + BX
Combustion
CxHy + O2  CO2 + H2O

12. Synthesis Reactions A + X  AX
Binary Ionic Compounds
Formation of Metal Hydroxides

13. Reaction of Metals with Nonmetals A + X  Binary Compound
Example 1
Mg + O2 
Example 2
Fe + O2 
Example 3
Na + Cl2 
MgO (Not Balanced)
FeO or Fe2O3 (Not Balanced)
NaCl (Not Balanced)

14. Synthesis Reactions of Metal Oxides w/ Water
MxOy + H2O  Mx(OH)y
metal oxide + water  metal hydroxide
Example 1
CaO + H2O 
Ca(OH)2

15. Decomposition AX  A + X Binary Compounds Metal Carbonates
Metal Hydroxides
Metal Chlorates
Oxyacids

16. Decomposition of Binary Compounds
AX  A + X
Example 1
HgO 
Example 2
H2O 
Hg + O2 (Not Balanced)
H2 + O2 (Not Balanced)

17. Decomposition of Metal Carbonates
MCO3  MO + CO2
metal carbonate  metal oxide + carbon dioxide
Example 1
CaCO3 
CaO + CO2
Poo Poo and Pee Pee

18. Decomposition of Metal Hydroxides
MOH  MO + H2O
Metal hydroxide  metal oxide + water
Example 1
Ca(OH)2 
CaO + H2O

19. Decomposition of Metal Chlorates
M(ClO3)  MCl + O2
metal chlorate  metal chloride + oxygen
Example 1
KClO3 
KCl + O2 (Not Balanced)

20. Decomposition of Acids Acid  Nonmetal Oxides + H2O
Example 1
H2SO4 
Example 2
H2CO3 
SO3 + H2O
CO2 + H2O

21. Single Replacement Reactions A + BX  AX + B Y + BX  BY + X
Replacement of a Metal by another Metal
Al + Fe(NO3)3 
Replacement of Hydrogen in Water by a Metal
Na + H2O 
Fe + Al(NO3)3
NaOH + H2
Must check the activity series to make sure the lone element has a greater activity than the element in the compound.

22. Can react with steam and acids, replacing the hydrogen.
lithium
Potassium
barium
strontium
calcium
sodium
magnesium
aluminum
zinc
chromium
iron
cadmium
cobalt
nickel
tin
lead
Hydrogen
antimony
arsenic
bismuth
copper
mercury
silver
paladium
platinum
gold
Can react with cold water and acids, replacing hydrogen. Will form Metal Hydroxide and Hydrogen when added to water.
Can react with steam and acids, replacing the hydrogen.
Can react with acids, replacing the hydrogen.
React with oxygen, forming oxides.
Fairly unreactive. Form oxides only indirectly.

23. Single Replacement Reactions
Replacement of Hydrogen in an Acid by a Metal
Mg + HCl 
Replacement of Halogens
Cl2 + KBr 
MgCl2 + H2
KCl + Br2

24. Double Replacement Reactions AX + BY  AY + BX
Positive Ions (cations) in Both Compounds Switch Places
Positive Ions are Written First
Pb(NO3)2 + KI 
HCl + NaOH 
PbI2 + KNO3
NaCl HOH
HOH = H2O

25. Combustion : Complete CxHy(Oz) + O2  CO2 + H2O
C2H6 + O2  C6H6O2 + O2 
CO2 + H2O
CO2 + H2O
Combustion: InComplete
CxHy(Oz) + O2  CO + H2O