ICSE Class 10 Answered

These reactions are of two types:

Precipitation reactions and Neutralisation reactions.

Precipitation reactions

The insoluble solid formed during the double displacement reactions is called a precipitate. Reactions in which a precipitate is formed as one of the products are also called precipitation reactions.

Sodium sulphate reacts with barium chloride to form barium sulphate and sodium chloride solution.    

                Na₂SO_{4 (aq)}   +   BaCl₂   →        BaSO_4(s)    +      2NaCl_(aq)

                Sodium            Barium                Barium              Sodium

Decomposition reaction

A chemical reaction in which a single compound splits into two or more simple substances is called a decomposition reaction.

When the mercuric oxide is heated in a crucible, the orange-red powder begins to darken and a silver mirror begins to deposit on the cooler parts of the crucible. This is mercury. If we hold a glowing splint near the crucible, it can relight. This shows that the gas evolved during the reaction is oxygen.

2HgO_(s)                   →            2Hg_(s)     +    O₂ ↑

Mercuric oxide                   Mercury     Oxygen

The difference between decomposition and double decomposition reaction is in decomposition reaction there is only one reactant and in double decomposition reaction, there are two reactants.