1. Unit 3: Balancing Equations, Types of Reactions
Chapter 8

2. Key Concepts Chemical Reactions: Reactants yield Products
Balancing Chemical Equations (coefficients)
Writing Equations (subscripts + coefficients)
Types of Reactions:
Synthesis
Decomposition
Combustion
Single-Replacement
Double-Replacement (precipitation)

3. Chemical Reactions
Chemical Reaction: substances change into new substances with different physical and chemical properties
Reactants: go into a chemical reaction
Products: come out of a chemical reaction

4. Chemical Equations
Chemical Equation: shows the balanced formulas of the reactants and products
Reactants
Products
Chemical Equation
According to the law of conservation of mass, the amount of reactants is equal to the amount of products.
[yield]

5. Chemical Equation Symbols
Meaning
(s), (l), (g)
The substance is in a solid, liquid, or gaseous state
(aq)
The substance is in an aqueous solution (it’s dissolved in water)
Indicates the results of a reaction; “yields”
Reversible reaction where the result is
a mix of both products and reactants
heat
The reaction requires heat to occur

6. Subscripts & Coefficients
Subscript: the number of atoms in a molecule
Coefficient: the number of molecules

7. Ca(s) + 2H2O(l)  Ca(OH)2(aq) + H2(g)
Chemical Equations
In the following equation, label the reactants, products, subscripts, coefficients, and phases
Ca(s) + 2H2O(l)  Ca(OH)2(aq) + H2(g)
REACTANTS PRODUCTS
Green = Phases Orange = Coefficients
Purple = Subscripts
Calcium + Water = Calcium Hydroxide + Hydrogen gas
One significant application of calcium hydroxide is as a flocculant, in water and sewage treatment.

8. Balancing Equations (coefficients)
Ex.
___ C + ___ O2  ___ CO
___ H2 + ___ N2  ___ NH3
Tip: start with something that appears only once on each side
___ CH4 + ___ O2  ___ CO2 + ___ H2O
Tip: start with C or H because they only appear once on each side
2 C + 1 O2  2 CO
3 H2 + 1 N2  2 NH3
1 CH4 + 2 O2  1 CO2 + 2 H2O

9. Writing Chemical Equations
Write Skeleton Equation
Subscripts
Elements  check Br2I2N2Cl2H2O2F2
Ionic Compounds  Balance Charges
Coefficients
Balance Equation
Ionic Compounds = Balance Charges

10. Writing Equations (subscripts + coefficients)
Ex. hydrogen was combined with oxygen to yield water
Ex. nitrogen and hydrogen yield ammonia (NH3)
Ex. aluminum bromide plus chlorine yield aluminum chloride plus bromine
2 H2 + O2  2 H2O
N2 + 3 H2  2 NH3
2 AlBr3 + 3 Cl2  2 AlCl3 + 3 Br2

11. Types of Reactions Synthesis Reactions Decomposition Reactions
Combustion Reactions
Single-Replacement Reactions
Double-Replacement (precipitation) Reactions

12. Synthesis Reactions A + B  AB
Synthesis: simple substances are combined to make a more complex substance
A + B  AB

13. Decomposition Reactions
Decomposition: a complex substance breaks apart into simpler substances
Many explosives show violent decomposition
AB  A + B

14. Combustion Reactions A + O2  AXOY CXHY + O2  CO2 + H2O
Combustion: a substance burns in oxygen to form oxides
Combustion with a hydrocarbon will always produce CO2 + H2O
A + O2  AXOY
CXHY + O2  CO2 + H2O

15. Single-Replacement Reactions
Single-Replacement: a metal or a nonmetal element reacts with an ionic compound
A + XY  X + AY

16. Double-Replacement Reactions
Double-Replacement (precipitation): two ionic compounds react to produce at least one insoluble product
AB + XY  XB + AY