Date: Sept 19
Sections 6.6, 6.7, 6.10

Reaction Types

There are five main chemical reaction types. Each causes the molecules of the reactants to be rearranged in a different fashion. The following list will follow your text book with a page reference.

Combustion

Combustion is the reaction of any material with oxygen. It is what is normally called "burning". Combustion reactions are very rapid reactions that produce heat, light and compounds called oxides. Most controlled combustion reactions use a "fuel" to react with oxygen to produce energy. The most common fuels are hydrocarbons or petroleum derivatives. Examples are; propane, gasoline, kerosene, etc.
When a hydrocarbon is burned it releases carbob dioxide (CO2) and water vapour (H2O) if complete combustion occurs. If there is not enough oxygen available then unnecessary byproducts are produced. Carbob dioxide and water are still produced but so also is carbo monoxide (CO) and carbon (C) which is usually in the form of soot & smoke.

Synthesis

Synthesis reactions involve the formation of new product which is the molecular sum of the reactants. Two or more smaller molecules join together to form a larger, more complex molecule.

  1. Direct union of two elements will produce a binary compound.
  2. Metallic oxides and carbon dioxide react to produce carbonates.
  3. Binary salts and oxygen react to produce a chlorate.
  4. A metallic oxide or a nonmetallic oxide combine to form a base or acid respectively.

Examples of each are as follows:

  1. Mg + O2 ---> MgO
    H2 + O2 ---> H2O
    K + Cl2 ---> KCl
    Fe + O2 ---> Fe2O3

  2. CaO + CO2 ---> CaCO3
    Na2O + CO2 ---> Na2CO3

  3. KCl + O2 ---> KClO3

  4. CaO + H2O ---> Ca(OH)2
    Na2O + H2O ---> NaOH
    N2O5 + H2O ---> HNO3
    P2O5 + H2O ---> H3PO4

Here's some example for you to try

  1. LiCl + O2 --->
  2. Na2O + CO2 --->
  3. SO3 + H2O --->
  4. N2 + H2 --->

Decomposition

Decomposition reaction involve the breaking apart of a large molecule into smaller, simpler molecules or the atoms that make up the larger molecule. Decomposition reactions tend to be difficult to predict the precise products produced and may actually have to be memorized.

A few examples:

Single Dispacement

During single replacement, one element replaces another element in a compound. There are two different possibilities: First variation: One cation replaces another. Written using generic symbols, it is:

AX + Y ---> YX + A

Element Y has replaced A (in the compound AX) to form a new compound YX and the free element A. Remember that A and Y are both cations (postively-charged ions) in this example.

Some examples are:

Notice how, when hydrogen gets displaced, it is written as a diatomic gas. Don't forget that!!

Second variation: one anion replaces another. Written using generic symbols, it is:

A + XY ---> XA + Y

Element A has replaced Y (in the compound XY) to form a new compound XA and the free element Y. Remember that A and Y are both anions (negatively-charged ions) in this example .

Here are two examples that involve halogens:

  1. Cl2 + NaBr ---> NaCl + Br2
  2. Br2 + KI ---> KBr + I2

In single replacement, one reactant is always an element. It does not matter if the element is written first or second on the reactant side. The other reactant will be a compound.

Typically, you will be given the left-hand (reactant side) and asked to provide the products to the reaction. You need to be able to recognize single replacement reactions AND be able to break a formula apart into proper cations and anions as well as write correct formulas

Here are several examples for you to try.

  1. ZnS + O2 --->
  2. K + H2O --->
  3. Fe + HCl --->
  4. NaI + Br2 --->

Double Dispalcement Reactions

During double replacement, the cations and anions of two different compounds switch places.

Written using generic symbols, it is:

AB + XY ---> AY + XB

A and X are the cations (postively-charged ions) in this example, with B and Y being the anions (negatively-charged ions).

Some examples are:

  1. KOH + H2SO4 ---> K2SO4 + H2O
  2. FeS + HCl ---> FeCl2 + H2S
  3. NaCl + H2SO4 ---> Na2SO4 + HCl
  4. AgNO3 + NaCl ---> AgCl + NaNO3

In many cases of double displacement one of the products is a precipitate, ie. a solid forms. Knowing what the precipate is enables you to predict whether or not the reaction will take place.
There are two special caes of double displacement reactions: a) neutralization and b) displacement with decomposition.
a) In neutralization an acid react with a base to produce water and a salt.
An example would be

H2SO4 + NaOH -----> Na2SO4 + H2

b) Whenever H2CO3, H2SO3, or NH4OH is a product formula, the correct technique is to write the products as done in the examples. Don't forget that!! Here are three examples:

  1. CaCO3 + HCl ---> CaCl2 + CO2 + H2O
  2. K2SO3 + HNO3 ---> KNO3 + SO2 + H2O
  3. NH4Cl + NaOH ---> NaCl + NH3 + H2O
Under this rule the following reaction as written would be inncorrect.

CaCO3 + HCl ---> CaCl2 + H2CO3

Here are some examples for you to try

  1. Ca(OH)2 + HCl --->
  2. Al(NO3)3 + H2SO4 --->
  3. Pb(NO3)2 + K2S --->
  4. Pb(NO3)2 + CuSO4 --->

Make sure you try the examples in the text book and the work sheets.

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