1. Chapter 6: Chemical Reactions Occur in Predictable Ways
1. Synthesis Reactions
Occur when two or more reactants (usually elements) join to form a compound.
General Formula:
A + B  AB
(where A and B represent elements)

2. …can produce ionic or covalent compounds
Magnesium metal reacts with oxygen
gas to form magnesium oxide.
2Mg + O2  2MgO
Covalent:
Nitrogen gas and oxygen gas join to form dinitrogen monoxide.
2N2 + O2  2N2O

3. 2. Decomposition are the opposite of synthesis reactions
A compound breaks down into two or more products (often elements).
General Formula:
AB  A + B
(where A and B represent elements)

4. Ionic and Covalent Compounds can decompose
Table salt, sodium chloride, can be broken down into sodium metal & chlorine gas by melting salt at 800ºC and running electricity through it.
2NaCl  2Na + Cl2
Covalent:
By running electricity through water,
the water molecules decompose into
hydrogen & oxygen gases.
2H2O  2H2 + O2

5. 3. Single Replacement
When one element from a compound is replaced with a separate element
Two types, based on whether the single element is a metal or a non-metal
General Forms:
A + BC  B + AC where A is a metal, or
A + BC  C + BA where A is a non-metal

6. The Two Types: When A is a metal:
Aluminum foil in a solution of copper II chloride produces solid copper and aluminum chloride.
Al + CuCl2  Cu + AlCl3
When A is a non-metal:
When fluorine is bubbled through a sodium iodide solution, iodine and sodium fluoride are produced.
F2 + NaI  I2 + NaF

7. 4. Double Replacement
elements swap places between two compounds to form two new compounds.
Two ionic solutions react to form a precipitate (solid) and another ionic solution
General Form:
AB + CD  AD + CB

8. Double Replacement Example:
potassium chromate and silver nitrate react to form a red precipitate, silver chromate, in a solution of potassium nitrate.
K2CrO4(aq) + AgNO3(aq)  Ag2CrO4(s) + KNO3(aq)
Note: the K and Ag switch places in the compounds.

9. 5. Neutralization (aka Acid-Base reactions)
occur when an acid and a base react to form a salt and water.
acids (start with H)
bases (end in OH, or begin with NH4)
General Form:
Acid + base  salt + water
HX + MOH  MX + H2O
(where X and M are elements)

10. Neutralization Examples:
Sulphuric acid is used to neutralize calcium hydroxide:
H2SO4 + Ca(OH) 2  CaSO4 + 2H2O
Phosphoric acid helps to neutralize the compounds that cause rust, such as iron (II) hydroxide.
2H3PO4 + 3Fe(OH)2  Fe3(PO4)2 + 6H2O

11. 6. Combustion occurs when a compound or element reacts with oxygen
Always makes CO2 and H2O (in grade 10 examples)
Aka. hydrocarbon combustion
General Form:
CXHY + O2  CO2 + H2O

12. Combustion Examples: CH4 + O2  CO2 + 2H2O
Natural gas (methane) is burned in furnaces to heat homes
CH4 + O2  CO2 + 2H2O
An acetylene torch is used to weld metals together
2C2H2 + 5O2  4CO2 + 2H2O
Carbohydrates like glucose combine with oxygen in our body to release energy
C6H12O6 + 6O2  6CO2 + 6H2O

13. Take the Section 6.1 Quiz