Just as a symbol represents an atom of an element and a formula for a molecule of a substance, so chemical equations represent an actual chemical reaction.
Different molecules participate in a chemical reaction and new types of molecules are formed after the exchange of atoms or countries present in them. All these molecules can be represented by formulas.
The reaction of sodium chloride and silver nitrate can be represented as follows with the help of formulas.
AgNO3 + NaCl → AgCl + NaNO3
Here AgNO3 and NaCl are the reactants and AgCl and NaNO3 are the resultant or product. Representing a chemical reaction in this way is called a chemical equation.
Representing the reactants participating in a chemical reaction and the products or resultant substances resulting from the reaction by symbols and formulas is called chemical equation.
The reaction of hydrochloric acid on calcium carbonate forms calcium chloride and water and carbon dioxide is released.
CaCO3 + 2HCl → CaCl2 + H2O + CO2
What is the Method of writing Chemical Equation
While writing the chemical equation of a reaction, the following points should be kept in mind –
1) The names and chemical formulas of the reactants and products of the reaction should be known.
2) Substances are always written in the form of molecules in an equation. For example, hydrogen, nigtogen, oxygen and chlorine etc. are written as H2, N2, O2 and Cl2 respectively, because all these gases are diatomic. Elements of a mono atomic are written by their symbols. Like sodium, magnesium and copper are written as Na, Mg and Cu respectively.
3) The reactants participating in a chemical reaction are written on the left side by symbols or formulas and a plus (+) sign is put between the different reactants. For example, magnesium metal (Mg) burns in oxygen (O2). For this the left side will be Mg + O2.
4) The products obtained after chemical reaction are written by symbols or formulas on the right side and plus (+) sign is put between different products.
For example, the product in the appropriate reaction is magnesium oxide. Hence MgO will be written on the right side.
5) Then an equal (=) or an arrow (→) sign is placed between the reactants and the products.
Mg + O2 → MgO
This equation is called the skelton equation. Finally this skelton equation is balanced.
Balancing the Equation
The number of atoms of each element on the left and the right side of the chemical equation should be equal, because according to the law of conservation of mass, neither an atom is lost nor a new atom is created in every chemical change.
So we should equalize the number of atoms of the element in both the sides of the above equation in the following way –
i) First of all we see that one molecule of oxygen has two atoms of oxygen which will form two molecules of magnesium oxide.
Mg + O2 → 2MgO
We call the above equation as the chemical equation because the number of atoms of each element is equal on both its sides.
Balanced Chemical Equation
A chemical equation in which the number of atoms of each element is equal on both sides is called a balanced chemical equation.
2KClO3 → 2KCl + 3O2
NH3 + HCl → NH4Cl
Zn + H2SO4 → ZnSO4 + H2
H2 + Cl2 → 2HCl
Methods of Balancing Chemical Equation
Following are the four methods of balancing the Chemical Equation :-
Trial and error method
Partial equation method
Ionic Equation method
Trial and Error method
First the reactants are written on the left side of the arrow and the products are written in the form of their formulas on the right, then the atom which has come in the least number is first balanced. After this balance the number of atoms in increasing order.
Example: The reaction of concentrated sulfuric acid (H2SO4) on copper (Cu) gives copper sulfate (CuSO4), sulfer dioxide (SO2) and water (H2O).
Cu + H2SO4 → CuSO4 + SO2 + H2O