The chemical reaction which is expressed by using molecular formulae of reactants and products is called chemical equation. The chemical equation is also called formula equation. The representation of chemical reaction becomes easy.
2 H2 + O2→2 H2O
Skeletal chemical equation
The chemical equation in which the total number of atoms of each element in reactant and product is not equal is called an unbalanced chemical equation or skeletal chemical equation. Some examples:
Drawbacks of skeletal chemical equation
There are many unbalanced chemical equations which need to be balanced. Mostly, we balance the chemical equation by comparing the numbers of atoms in reactant and product molecules and then equalizing the both sides. Balanced chemical equation is a type of equation in which a total number of atoms in reactants and products are equal. It is based on the law of conservation of mass.
Hydrogen and oxygen react with eachother to produce water.
Hydrogen + Oxygen→ Water
H2 + O2→ H2O (Skeletal equation)..........(i)
2H2 +O2→ 2H2O (Balanced chemical equation).............(Ii)
In the above equation (ii), the total number of atoms in reactant and product are equal so it is a balanced chemical equation.
Balancing a Chemical Equation
There are various ways to balancea chemical equation. But simplest one is Hit and trial method which is explained below:
When ethane is burnt in oxygen, carbon dioxide gas and water are produced.
Ethane + Oxygen → Carbon dioxide + water(Word Equation)
C2H6 + O2 → CO2 + H2 (Skeletal Equation)
2C2H6 + 7O2 → 4CO2 + 6 H2O (Balanced Equation)
The chemical reaction that occurs only in one direction is called irreversible reaction. For example, when calcium carbonate is being strongly heated, it decomposes to calcium oxide and carbon dioxide.
Calcium carbonate → Calcium oxide + Carbon dioxide
CaCO3 → CaO + CO2↑
The chemical reaction that occurs both in forward and backward directions is called reversible reaction.
Nitrogen + Hydrogen \(\rightleftharpoons\) Ammonia
N2 + H2 \(\rightleftharpoons\) NH3
The chemical equation written by balancing the number of atoms of elements on both sides of the reactants and products is called balanced chemical equation.
Following information can be obtained from a balanced chemical equation:
The reaction which occurs in forward and backward directions is called reversible reaction. For example:
N2 + 3H22NH3
The chemical reaction which occurs only in forward direction is called irreversible reaction. For example:
CaCO3 → CaO + CO2
The reaction which absorbs heat during the chemical change is called endothermic reaction. For example:
2KClO3 + Heat → 2KCl + 3O2
CaCO3 + Heat → CaO + CO2
NaNO2 + NH4Cl + Heat → NaCl + 2H2O + N2
The reaction which evolves heat during the chemical change is called exothermic reaction. For example:
C + 2H2 → CH4 + Heat
C + O2 → CO2 + Heat
The information that cannot be obtained from a balanced chemical equation are:
The method for writing balanced chemical equation are: