Core Tips

1. Chemical reactions involve a chemical change.

2. During a chemical change, bonds between the atoms of reactants break and new bonds between the atoms of the products are formed. The number of atoms of all the elements remains the same.

3. Chemical reactions can be classified into following categories. Each category has its own characteristics. (i) combination reactions (ii) decomposition reactions (iii) double decomposition reactions (iv) neutralization reactions (v) displacement reactions (vi) redox reactions

4. In a combination reaction, two or more substances combine to form a single product. e.g. 2 Mg + O2 → 2 MgO

5. In a decomposition reaction, a substance breaks up into two or more simple substances. e.g. CaCO3 → CaO + CO2

6. In a double decomposition reaction, the cations and the anions of the two compounds mutually exchange their positions to form two new com- pounds. e.g. PbCl2 + 2 KI → PbI2 + 2 KCl

7. In a neutralization reaction, an acid reacts with a base ( or alkali ) to form salt and water. e.g. HCl + NaOH → NaCl + H2O

8. In a displacement reaction, a more active element displaces a less active element from its solution. e.g. Zn + FeSO4 → ZnSO4 + Fe

9. In an oxidation reaction, there is a removal of hydrogen or addition of oxygen and in a reduction reaction, there is removal of oxygen or addition of hydrogen atom. Oxidation and reduction reactions take place simultaneously.

10. Different chemical reactions take place with different rates. The rate of a chemical reaction is affected by factors like nature of reactants, size of particles, concentration of substances, temperature and use of catalyst etc.

11. A catalyst increases the rate of a chemical reaction. In many industrial processes, catalysts are used for profitable productions.