Lakhmir Singh Science Chapter 6 Physical and Chemical Changes Class 7

Lakhmir Singh Chapter 6 Physical and Chemical Changes

 

Book – Class 7 Science

Author – Lakhmir Singh Sir

Very short answer type questions

 

{1} Zinc

{2} Carbon, Chromium and Nickel

{3} Crystallization

{4} a-Evaporation b- crystallization

{5} Copper Sulphate

{6} Carbon Di-oxide {CO2}

{7} True or False

1. False
2. False
3. True
4. False
5. True

{8}

1. Photosynthesis – Chemical Change
2. Burning of Coal – Chemical Change
3. Digestion of Food – Chemical Change
4. Dissolving of Sugar in Water – Physical
5. Melting of Wax – Physical
6. Beating Aluminum to Make Aluminum Foil-Physical

 

{9} physical or chemical change

1. Glass Bottle breaking – Physical
2. Making a cake -Chemical change
3. Wool knitted into sweater – Physical
4. Burning of incense stick – Chemical
5. Tearing of paper – Physical
6. Cooking of food – Chemical
7. Formation of Clouds – Physicals
8. Drying of clothes – Physical
9. Burning of Paper – Chemical
10. Formation of Rust – Chemical

 

{10} fill in the blanks

1. Chemical
2. Physical, chemical
3. Chemical
4. Sodium hydrogen bicarbonate
5. Calcium carbonate
6. Painting and galvanization
7. Galvanization
8. Salt
9. Crystallization.

 

Short answer type questions:

{11} Iron grill is painted frequently to prevent it from rusting as an iron grill interacts with moisture and oxygen it constantly forms rust.

 

{12} Iron pipes are coated with zinc to prevent them from rusting because zinc is not affected by water.

 

{13} If some grease or oil is applied to a surface of an iron object, it prevents air and moisture from coming into contact with it, thus rusting is prevented.

 

{14} Painting an iron gate prevents it from rusting, as air and water cannot be in contact with the surface of the iron object, so rusting cannot take place.

 

{15} The reason is that the air in those palaces contains more water vapor.

 

{16} The process of coating iron objects with a thin layer of zinc metal is called galvanization. In this process, iron sheets are dipped in molten zinc and then allowed to cool.

 

{17} Rust can be prevented in two ways:

(a) Iron can be protected from rust by painting.

(b) Iron can be prevented from rusting by applying grease or oil.

 

{18} Stainless steel is a material made from iron. Carbon, chromium, and nickel are added to iron to produce stainless steel, which does not rust.

 

{19} Differences between physical and chemical change are as follows:

Physical	Chemical
New substance is not formed in this change	new substance is formed in this change
This change is temporary	This change is permanent
it is easily reversible	it is non reversible
Less energy is absorbed in this	lot of energy is absorbed in this

 

{20} Iron (Fe) + Oxygen (O₂) + Water (H₂O) à Iron oxide (Fe₂O₃)

 

{21} The explosion caused by fireworks, such as crackers, is a chemical change that cannot be reversed.

 

{22} The melting of ice into water is called a physical change since it can be a reversible change.

 

{23} Obtaining crystals from a hot, concentrated solution is called crystallization.

 

{24} The process of cooling a hot, concentrated solution of a substance to obtain crystals is called crystallization. Copper sulphate crystals are prepared by crystallization.

 

{25} (a) The burning of magnesium ribbon in air produces magnesium oxide.

(b) The melting of ice into water.

Long Answer Type Question Solution:

 

(26) Physical Change: – Any change in which no new substances are formed is known as a physical change. Example: Wax Melting , glass broken.

Chemical change: – When new substances are formed, it is called a chemical change. Example: – Cooking of food,burning of dry leaves.

 

(27) Rust forms when iron is exposed to damp air or water for a long period of time. This is called rusting of iron.For iron to rust, it needs oxygen and water .Objects made of iron rust over time as iron slowly damage itself.

 

(28) In the presence of copper sulfate solution, iron nails produce green-colored iron sulfate solution and brown deposits of copper on their surfaces.

Copper Sulphate Solution (Blue) + Iron (Grey) –> Iron sulfate solution (Green) + Copper (Brown).Chemical changes occur here.

 

(29) The mixing of baking soda and vinegar produces bubbles of carbon dioxide gas, as well as other substances.

Sodium hydrogen carbonate (Baking Soda) + Acetic acid (Vinegar) = Sodium Acetate + Carbon di oxide + water.Chemical changes are involved here.

 

(30) CaCo3 is formed when calcium hydroxide is combined with carbon dioxide.

Ca(OH2) + CO2 = CaCo3 + H2O – Chemical changes are taking place here.

 

(31) It’s a chemical change because it forms carbon dioxide as one of the new substances. In chemical change new substance is formed.

 

(32) There are both physical and chemical changes that occur when a candle burns. On heating, candle wax melts and forms liquid wax. It is a physical change.When the wax vapor burns, new substances are formed such as carbon dioxide.

(33) A reversible change in which the properties of the matter do not change.

Burning wood is considered a chemical change because new substances are formed. And not reversible.

A change in which matter undergoes an irreversible change and it forms a new substance.

However, cutting wood is considered to be a physical change since no new substances are formed only their shape changes.

 

(34) Magnesium oxide is formed when magnesium ribbon is burned in air.

Mg + O_{2 =} mgo – This is a chemical change.

 

(35)  Magnesium hydroxide is formed when magnesium oxide is dissolved in water.  Mgo + H₂O = Mg(OH)₂

Hi

Myself Shanaya More, I am a student of Class 7 and I wrote all the answers for this chapter, if you find any answer incorrect then please tell us.