CBSE Class 7 Science Changes and Reactions Assignment

I. Choose the correct answer:

1) An acid reacts with a base to form a salt & water. This type of reaction is called

a) Combination reaction b) Neutralization reaction

c) Displacement reaction d) Decomposition reaction

2) Curdling of milk is a

a) Chemical change b) Physical change c) Both (a) & (b) d) None of these

3) Rusting takes place in

a) Air-free moisture b) Moisture-free air c) Moist air d) None of these

4) The digestion of food is a

a) Physical change b) Chemical change c) Both (a) & (b) d) None of these

II. Fill in the blanks.

1) Melting of wax is a _______ change.

2) Cooking of food is a _______ change.

3) In a ___________ reaction, two or more reactants add up to form a product.

4) The forming of rust is called _______.

5) Hydrocarbons are compounds made of _____ and _______.

III. State true or false.

1) When a substance is burnt only light is emitted.

2) Magnesium combines with oxygen of air to form magnesium oxide.

3) New substances are formed in a physical change.

4) The mixture of water and alcohol forms a heterogeneous mixture.

5) Petrol, diesel and LPG contain mixtures of hydrocarbons.

IV. Match the following.

                A                                                   B

1) Electromagnets                               a) baking soda

2) Nichrome                                        b) steel

3) sodium hydrogencarbonate            c) heating element

4) metallic solids                                 d) red-brown solid

5) rust                                                 e) washing machines

V. Define.          

1) Physical change 2) Chemical change 3) Melting 4) Freezing

5) Vaporisation 6) Condensation 7) Rusting 8) Combination reaction

9) Decomposition reaction 10) Displacement reaction 11) Neutralization reaction

VI. Give reasons

1) Freshly cut apple or brinjal turns brown.

2) Burning of magnesium ribbon is considered a chemical change