Define the following :

1. Reactants.

Ans. Substances undergoing a chemical change are called as reactants. 


2. Products.

Ans. The new substance formed as a result of chemical reaction is called as product.

3. Word equation.
Ans.
The simple form of representation of chemical reaction in words is word equation.

4. Chemical equation.
Ans.
The representation of chemical reaction with the help of chemical formulae is a chemical equation.

5. Combination reaction.
Ans.
When two or more substances combine (mixture or compounds) to form a single product, then the reaction is called as combination reaction.

6. Displacement reaction.
Ans.
When a more reactive element removes another element, having less reactivity, from its compound, this reaction is called as displacement reaction. 

7. Decomposition reaction.
Ans.
When a single reactant has broken down to give a simple product is known as decomposition reaction.

8. Double displacement reaction.
Ans.
The reaction where a precipitate is formed by exchange of ions between the reactants is called as double displacement reaction. OR

A chemical reaction in which constituents (radicals or ions)of two substances mutually exchange their places to form two new substances is called as double displacement reaction.

9. Redox reaction.
Ans.
When oxidation and reduction takes place simultaneously in a given chemical reaction, it is called as redox reaction.

10. Oxidation reaction.
Ans.
The chemical reaction in which reactants gain oxygen to form corresponding oxide. Similarly

A chemical reaction in which reactants lose hydrogen to form product is called oxidation.

11. Reduction reaction.
Ans.
The chemical reaction in which reactants gain hydrogen are reduction reactions. Similarly

The reaction in which reactants lose oxygen atom to form product is called reduction.

12. Neutralization reaction.
Ans.
The reaction between acid and alkali to form salt and water is called as neutralization reaction.

13. Corrosion.
Ans.
The slow process of decay or destruction of metal due to the effect of air, moisture, acids on it is called as corrosion.

14. Exothermic reaction.
Ans.
The reaction in which heat is evolved is called as exothermic reaction.

15. Endothermic reaction.
Ans.
The reaction in which heat is absorbed is called as endothermic reaction.

16. Balanced equation.
Ans.
When number of atoms are same on the L.H.S. and R.H.S. of the chemical equation, then the equation is said to be a balanced equation.