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Answer:
25. Iron is an object that frequently rusts when it comes in contact with water and air (O2). So iron grills are constantly exposed to those conditions. So to prevent them from rusting and losing their strength, they are painted frequently.
26. Iron pipes carrying water are coated with zinc to prevent them from rusting as Zinc on coming with contact with air or water forms a layer of oxide which is super resistant.
27. Iron parts and tools are smeared with grease or oil to prevent them from coming in contact with air or water and thus prevent them from rusting.
28. Rusting is a process that requires both water and air. In coastal regions, both the factors are available, so rusting is fast. But in deserts, due to intense heat, water evaporates and only air is left, which all alone is not sufficient to cause rusting.
29. The process of coating iron object with a layer of zinc to prevent them from rusting is known as Galvanisation. It is done to prevent rusting of iron.
30. Stainless steel is a special mixture that is prepared chemically and has not corrosive properties. It is an alloy made from Iron, Chromium, Silicon, Nickel, Carbon, Nitrogen and Manganese.
As it is an alloy, it has properties different from
iron and thus does not rust and also has properties which help it to get rid of stains.
31. Physical Change :
a. When a substance undergoes a physical change, its composition remains the same despite its molecules being rearranged.
b. It is a temporary change.
c. A physical change involves very little to no absorption of energy.
Chemical Change :
a. When a substance undergoes a chemical change, its molecular composition is changed entirely. Thus, chemical changes involve the formation of new substances.
b. It is a permanent change.
c. During a chemical reaction, absorption and evolution of energy take place.
32. Check the attachment for the equation.
33. Burning of explosive is a chemical change as it involves burning which is exchange of a lot of heat energy.
34. Melting of ice is said to be a physical change as it is a reversible process, and the molecular formula of water remains same.
35. Crystallization or crystallisation is the process by which a solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some of the ways by which crystals form are precipitating from a solution, freezing, or more rarely deposition directly from a gas.
36.
a. Burning of crackers.
b. Melting of ice.
Hope it helps.
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Answer:
iron is an object which frequently rust when it comes in the contact of water and air so iron grills are constantly exposed to those conditions. So to prevent them from rusting and losing their strength, they are painted frequently.
28. Iron pipes carrying water are cooled with zinc to prevent them from rusting as Zinc on coming with contact with air or water forms a layer of oxide which is super resistant
27. Iron ports and looks are smeared with grease or oil to prevent them from coming in contact
with air or water and thus prevent them from rusting 28. Rusting is a process that requires both water and air. In coastal regions, both the factors are
available, so rusting is fast. But in deserts, due to intense heat, water evaporates and only air is left
which all alone is not sufficient to cause rusting
29. The process of coating iron object with a layer of zinc to prevent them from rusting is known as Galvanisation. It is done to prevent rusting of iron.
30 Stainless steel is a special mixture that is prepared chemically and has not corrosive properties. It is an alloy made from tron. Chromium. Silicon. Nickel, Carbon, Nitrogen and
Manganese.
As it is an alloy, it has properties different from
Iron and thus does not rust and also has properties which help it to get rid of stains.
31. Physical Change
a. When a substance undergoes a physical change. Its composition remains the same despite its
molecules being rearranged.
b. It is a temporary change.
CA physical change involves very little to no absorption of energy
Chemical Change:
a. When a substance undergoes a chemical change, its molecular composition is changed entirely Thus, chemical changes involve the formation of new substances.
b. It is a permanent change.
C. During a chemical reaction, absorption and evolution of energy take place.
32. Check the attachment for the equation
33 Burning of explosive is a chemical change as it involves burning which is exchange of a lot of
heat energy.
34. Melting of ice is said to be a physical change as it is a reversible process, and the molecular
formula of water remains same.
35. Crystallization or crystallisation is the process by which a solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some of the ways by which crystals form are precipitating from a solution, freezing, or more rarely deposition directly from a
gas
36.
a Ruming of crackers.
b. Melting of ice
Hope it helps