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Grade 11 Chemistry: Unit 1: Matter and Chemical Bonding

Balancing Equations/ Chemical Reactions

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Balancing Equations/ Chemical Reactions

Here, you will learn how to balance a chemical reaction and state the type of reaction that occurred.

Types of Chemical Reactions

There are 5 main types of chemical reactions:

Combustion: The resulting products are always Oxygen, (CO2) and Water, (H2O)
Single Displacement: A + BC-----> AC + B
Double Displacement: AB + CD -----> AD + BC
Synthesis: A + B -----> AB
Decomposition: AB-----> A + B
 
Combustion
Combustion is quite simple. As long as there is Oxygen, Hydrogen and Carbon in the reactants, it creates Water and Hydrogen gas as the products.
 
Synthesis
Synthesis is basically taking the reactants, combining them, and creating a product. So, for example, we can take Magnesium and Oxygen. It is written as:
Mg + O2 ---> MgO
 
The oxidation states of Magnesium and Oxygen are both 2. We know this because Magnesium wants to lose 2 electrons to get a stable octet, and Oxygen wants to gain 2 electrons to become a stable octet. The overall charge of this bond is neutral. Since we can divide by a common factor of 2, it will be written as MgO.
 
Single Displacement
Single displacement written like this:
Li + MgO ---> Li2O + Mg
 
Basically, the lonely Lithium "kicks" out the Magnesium and bonds with Oxygen. In order for Lithium to kick out the Magnesium, it must be higher on the activity series than Magnesium, which it is. Lithium's oxidation state is 1, since it wants to lose 1 electron. Oxygen's oxidation state is 2 because it wants to gain 2 electrons. So, when you criss cross down, you get Li2O.
 

activityseries.jpg

Decomposition
Decomposition involves taking a compound and breaking it down into the individual atoms. Here is the format for doing so:
 
MgO ---> Mg + O2.
 
This is pretty basic, but decomposition can be a lot harder. The reason why Oxygen is O2 and not just O is because Oxygen is diatomic. This means that it always exists as O2. This is Oxygen gas.
 
Double Displacement
Double Displacement is like single displacement. The format, as stated above, is AB + CD ---> AD + BC
 
The outer molecules react with each other and the inner molecules react with each other. An example of this is:
 
MgO + LiO---> MgO + Li2O
 
It may not look like it, but this is a double displacement reaction. The reason why this may look confusing is because MgO(Magnesium Oxide) stayed the same. That's because it reacted with the outer Oxygen molecule of the Lithium Oxide bond.
 
Balancing
 
The balancing portion is pretty simple. Basically, you want to have the same amount of each atom on both sides of the equation, the reactant side, and the product side. so, for an equation like Li + O2 ---> Li2O it would be balanced and written like this:
4Li + O2---> 2Li2O
 
Note that on both sides of the equation, there are 4 Lithium atoms, and 2 Oxygen atoms. This chemical equation is now balanced.