Important Points:

  1. Chemical changes taking place in a substance is called chemical reaction.
  2. Chemical equation: representing chemical reaction by using symbols and formulas is known as chemical equation.
  3. The substances that undergoes chemical change in a reaction are called reactants
  4. The new substances that are formed during a chemical reaction are called products.
  5. In a chemical equation the number of atoms of elements on reactant side and product side are equal.
  6. Combination reaction: when two or more substances react to form a single product then it is called combination reaction.
  7. Decomposition reaction : when a single reactant breaks down to form two or more products then it is called decomposition reaction.
  8. Displacement reaction: when an element displaces another element from a compound then it is called displacement reaction.
  9. Double displacement reaction: A reaction in which exchange of ion takes place is called double displacement reaction.
  10. Precipitation reaction: The reaction in which an insoluble product settle down is called as precipitation reaction.
  11. Exothermic reaction: A reaction in which heat is evolved is called exothermic reaction.
  12. Endothermic reaction  : A reaction in which heat is absorbed is called endothermic reaction.
  13. Oxidation reaction:The gain of oxygen is called oxidation OR The loss of hydrogen is called oxidation.
  14. reduction reaction: The loss of oxygen is called reduction OR The addition of hydrogen is called reduction.
  15. Redox reaction: A reaction in which one reactant is oxidized and the other is reduced then the reaction is called redox reaction.
  16. Corrosion: Metals combine with oxygen in air in presence of moisture is called corrosion.
  17. Rancidity:Spoilage of food items due to oxidation is called rancidity.
Q1)select and write the most appropriate alternative from those given below each statement and rewrite the statement:
  1. The compound of silver used in black and white photography is Silver bromide.
  2. The exothormic reaction seen in all living organism is Respiration.
  3. The gas formed when Zinc reacts with hydrochloric acid is Hydrogen.
  4. The reaction in which their is action of ion between the reactants is called double displacement reaction .
  5. The oxidation of fats and oils that causes change in smell and taste of food stuffs is called Rancidity.

Q2)Name the following :
  1. The gas flushed on chip bags to prevent their oxidation.- Nitrogen
  2. Reaction in which energy absorbed -Endothermic reaction
  3. Damage caused to metals due to to moisture and air.-corrosion
  4. The compound formed when carbon dioxide combine with water in presence of light and chlorophyll.-Glucose
  5. Type of reaction in which single product is formed from two or more reactants.-combination reaction

1.State one use of calcium oxide.
Ans-Calcium oxide is used in making cement.

2. State any two methods to prevent rancidity
Ans-i)Adding antioxidants
        ii)Keeping food items in airtight containers.

3. state two examples of natural exothermic reaction
Ans-Respiration and decomposition of vegetables.

4.State what happens when magnesium ribbon is burnt.
Ans-Magnesium ribbon is burns with dazzling white light to form magnesium oxide.

5.State the type of reactions in the following:
i)Calcium Carbonate on heating breaks to give calcium oxide and carbon dioxide.
ii)Zinc reacts with copper sulphate to produce free copper.
Ans i)Decomposition reaction
       ii)Displacement reaction