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 and 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 and 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. 4. 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. 5. 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. 6. 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
Take the Section 6.1 Quiz