CBSE Class 10 Answered

Combination Reaction

When two or more substances combine to form a single product, the reaction is known as a combination reaction.

For example:                 

In the laboratory, iron sulphide is prepared by mixing iron and sulphur.

Fe_(s)    + S_(s)  →  FeS_(s)

Decomposition Reaction

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

For example:

When 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.

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

Mercuric oxide                    Mercury        Oxygen

Displacement Reaction

Reactions in which the more reactive element displaces the less reactive element from its compound are called displacement reactions.

For example:

Zinc displaces copper in copper sulphate to form zinc sulphate.

 Zn_(s)   +     CuSO_{4 (aq)}           →               ZnSO_{4 (aq)}   +       Cu_(s)

Zinc      Copper sulphate                      Zinc sulphate        Copper

Double Displacement Reaction

Reactions in which ions of the reactants exchange places to form two new compounds, are called double displacement reactions.

For example:

Sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water.

NaOH_(aq)      +         HCl_(aq)        →     NaCl_(aq)         +        H₂O_(l)