Page 112 - ICSE Chemistry 8

Example 2: Balance the following equa on.
Mg + O  MgO
2
Solu on: The above equa on is not balanced as the number of various atoms on both the sides is not
equal.

The balanced equa on for the equa on can be wri en as shown below.
2Mg + O  2MgO
2
The atomic masses of all the elements are shown below.
Mg = 24 u, O = 16 u

By using these atomic masses, we can fi nd the atomic masses of the compounds involved in
the reac on.
2Mg = 2 × 24 u = 48 u
O = 2 × 16 u = 32 u
2
2MgO = 2 (24 + 16) = 2 × 40 u = 80 u
Total mass of the reactants on LHS = 48 + 32 = 80 u
Total mass of the products on RHS = 80 u

Therefore, the total mass of the reactants is equal to the total mass of the products which
conforms to the law of conserva on of mass.
Therefore, the balanced equa ons 2Mg + O  2MgO
2
INFORMATION GATHERED FROM A CHEMICAL EQUATION

A chemical equa on provides us with only limited informa on about the chemical reac on it represents.

Let’s take an example of the following equa on to know about the informa on it provides.
CaCO  CaO + CO 2
3
Calcium carbonate Calcium oxide Carbon dioxide

The above equa on tells us about the following things.
• It tells us about the name of the reactant(s).

Reactant: CaCO 3
• It tells us about the name of the product(s).
Products: CaO and CO 2

• It tells us about the number of molecules of each reactant par cipa ng in the reac on.
1 molecule of calcium carbonate
• It tells us about the number of molecules of each product par cipa ng in the reac on.

1 molecule of calcium oxide and 1 molecule of carbon dioxide
• It tells us about the propor on of reactants.
Here, we have only one reactant.

• It tells us about the propor on of products.
Calcium oxide and carbon dioxide are in the ra o 1:1.

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