General Science 7th Class Chapter 5 Physical and Chemical Changes Solved Exercise

General Science

7th Class

Chapter 5

Physical and Chemical Changes

Questions

5.1 Encircle the correct option.

(i) Three of the following are alike. Select the one that is different from the others.

a. Solubility        b. Conductance        c. Oxidation        d. Boiling of a substance

(ii) A physical change occurs when:

a. Iron rusts        b. Solution of common salt is heated

c. A piece of wood burns        d. Sugar is heated strongly

(iii) A gas produced on heating solid potassium chlorate is:

a. Hydrogen        b. Carbon dioxide        c. Methane        d. Oxygen

(iv) Select all that happen during a chemical change.

a. A temporary change occurs

b. Composition of the substances is changed

c. Properties of the substances are changed

d. New substances with different properties are formed

(v) Freezing of a liquid is a:

a. Chemical change        b. chemical property        c. physical change        d. None of above

(vi) What are the products when electric current is passed through water?

a. only steam        b. hydrogen and steam        c. hydrogen and oxygen        d. oxygen and steam

(vii) A piece of iron is kept in open air for 5 days. A film of corrosion formed over it is:

a. iron oxide        b. iron sulphide        c. iron chloride        d. iron hydride

(viii) During combustion, a substance reacts with:

a. hydrogen        b. water        c. carbon dioxide        d. oxygen

(ix) The temperature at which a liquid's vapour pressure is equal to the external pressure surrounding the liquid is:

a. melting point        b. boiling point        c. freezing point        d. highest temperature

(x) Silver + Hydrogen sulphide + Oxygen → Silver sulphide + water

      The above reaction is known as:

a. combustion        b. rusting        c. tarnishing        d. dehydration

5.2 Define the following:

1. Physical change

2. Chemical change

3. Physical property

4. Chemical property

5. Melting point

6. Freezing point

7. Boiling point

8. Solubility

9. Rusting

10. Tarnishing

1. Physical change

Ans.

A change in the physical properties of a substance is called physical change.

2. Chemical change

Ans.

A change in the chemical properties of a substance is called chemical change.

3. Physical property

Ans.

A property due to the physical behaviour of the substance is called physical property.

4. Chemical property

Ans.

A property associated with the chemical structure of the substance is called chemical property.

5. Melting point

Ans.

Melting point is the specific temperature of a solid at which, it begins to melt.

6. Freezing point

Ans.

The temperature at which a liquid starts changing into solid is called freezing point.

7. Boiling point

Ans.

The specific temperature for a liquid at which, it begins to boil and converts from liquid state to gaseous state.

8. Solubility

Ans.

Solubility is the ability of a substance the (solute), to form a solution with another substance the (solvent).

9. Rusting

Ans.

It is a chemical change during which oxygen in the moist air reacts with the iron (Fe) to convert it into iron oxide (rust).

10. Tarnishing

Ans.

It is formation of thin film of corrosion that forms on the surface of objects made of silver, copper, brass, aluminum, magnesium, etc.