Chemistry
Give reasons why the following are considered as chemical changes.
Copper carbonate on heat gives copper oxide and carbon dioxide.
A bright light is seen evolved when a strip of magnesium is heated.
Sulphur when burnt in air evolves a gaseous acidic product.
An iron nail kept open in the atmosphere rusts.
A piece of magnesium strip is dropped into a beaker containing dilute hydrochloric acid.
Phy & Chem Changes
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Answer
Copper carbonate on heating gives copper oxide and carbon dioxide. As new products are formed and the change is irreversible hence it is a chemical change.
When a strip of magnesium is heated, magnesium oxide is produced and the bright light seen is the evolution of energy in the form of light. Hence, it is considered a chemical change.
Sulphur burns in air to produce a new gaseous acidic product [sulphur dioxide]. Hence, the change is a chemical change.
Iron nail kept in air forms rust [iron [III] oxide]. Iron [III] oxide is a new product and has different chemical composition and properties as compared to that of an iron nail. Hence, the reaction is a chemical change.
When a piece of magnesium strip is dropped into a beaker containing dilute hydrochloric acid, magnesium chloride is formed and hydrogen gas is liberated. As new products are formed and the change is irreversible hence it is a chemical change.
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Related Questions
Select the correct answer from the choice in bracket to complete each sentence:
A change in which a substance retains its identity is a …………… [physical/chemical] change.
Matter is added or removed during a …………… [chemical/physical] change.
Energy required for completion of a physical change is …………… [released/absorbed] when the change is reversed.
Dissolution of lead nitrate in water is deemed as a …………… [physical/chemical] change.
A change in which matter undergoes a change but the total mass of substance is unaltered is a …………… [physical/chemical] change.
State which of the following 1 to 5 pertain to —
A: Physical Change
B: Chemical change
Sublimation.
Fermentation.
Liquefaction or condensation.
Magnetization.
Respiration.
Match the examples of changes in List I with the correct type of change in List II.
List I List II 1. Burning of paper A: Physical change 2. Ringing of an electric bell B: Chemical change 3. Curdling of milk 4. An electric light is switched on. 5. Melting of butter Name the following:
The salt obtained when a chemical change takes place on addition of iron to dilute sulphuric acid.
The product obtained during a physical change when water converts from a liquid into a solid.
The product of the chemical change on keeping a polished iron nail exposed to the atmosphere.
A form of energy required for a chemical change.
The gaseous product of the chemical change which takes place during respiration in living organisms.