1. What is meant by Chemical combination?

            The reaction in which two or more substances combine to give a single substance is called Chemical combination.

eg:- S + O₂ → SO₂

       C + O₂ → CO₂

2. What are the different types of Chemical changes?

             The different types of Chemical changes are

1. Chemical combination 

2. Chemical decomposition

3. Chemical displacement

4. Chemical double decomposition

3. Give two examples for Chemical decomposition?

1. Decomposition of Calcium carbonate (CaCO₃)

            CaCO₃ decomposes on heating to form two substances - Calcium oxide (CaO) and Carbondioxide.

CaCO₃ → CaO + CO₂

2. Decomposition of hydrogen peroxide

            Hydrogen peroxide decomposes into water (H₂O) and oxygen (O₂).

2H₂O₂ → 2H₂O + O₂

4. What is meant by Chemical decomposition?

             The reaction in which a single substance split into two or more substances are called Chemical decomposition.

eg:-  CaCO₃  → CaO + CO₂

5. Give one example for Chemical displacement

              When Zinc is added to copper sulphate solution, Zinc displaces copper from CuSO₄ and forms colourless Zinc sulphate

Zn  + CuSO₄(Copper sulphate)  → ZnSO₄ (Zinc sulphate) + Cu

6. Define Chemical displacement

              The reaction in which one element or radical replaces another element or radical in a substance is called Chemical displacement.

eg:- Zn + CuSO₄ → ZnSO₄ + Cu

7. Explain the type of chemical change taking place in the reaction Br₂ + 2KI → 2KBr + I₂↑

               In the reaction Br₂ + 2KI → 2KBr + I₂, Bromine displaces Iodine from Potassium iodide liberating iodine gas. This is an example for chemical displacement reaction.

8. What is meant by chemical double decomposition?

               The reaction in which the elements exchange their radicals to form two new compounds is called double decomposition. 

eg:- BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl

9. Give two examples for chemical double decomposition reaction

              1.     AgNO₃ + NaCl → AgCl ↓ + NaNO₃ 

Silver (Ag) and Sodium (Na) exchange their constituents and form two new substances.

2.       BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl ; 

In this reaction barium (Ba) and Sodium (Na) exchange their anions to give two new compounds.

10. Give one example each for reversible and irreversible chemical double decomposition reaction

            Chemical changes are reversible and irreversible.

AgNO₃ + HCl →  AgCl + HNO₃

This reaction is irreversible ie, products donot combine to give reactants. 

PCl₅ ↔ PCl₃ + Cl₂

This reaction is reversible. The product can be changed to reactant depending upon experimental conditions.