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Class 7 Science Chapter 5 Question Answers - Physical and Chemical Changes

Q1: What is rust?

Ans : When iron oxide is hydrated, it is known as Rust(Fe2O3. XH2O)

Class 7 Science Chapter 5 Question Answers - Physical and Chemical Changes

Q2: What is added to steel to make it stainless?

Ans:  Stainless steel is made by mixing iron with carbon and metals like chromium, nickel and manganese.


Q3: What type of change is photosynthesis?

Ans : Chemical change

Class 7 Science Chapter 5 Question Answers - Physical and Chemical Changes

Q4: What is a chemical change?

Ans : A change, in which a new substance with different properties is formed, is known as a chemical change.


Q5: A change, in which a new substance with different properties is formed, is known as a _________________.

Ans : Chemical change


Q6: ___________is a property by virtue of which a metal can be beaten into thin sheets without breaking.

Ans : Malleability

Class 7 Science Chapter 5 Question Answers - Physical and Chemical Changes

Q7: Write the chemical formula of blue vitriol.

Ans : Crystals of copper sulphate pent hydrate (CuSO4.5H2O) are blue in colour. So, it is commonly known as blue vitriol.


Q8: State the two important conditions for rusting.

Ans : Presence of water and presence of oxygen


Q9: What is freezing point of water?

Ans : The freezing point is 0°C at which water freezes.


Q10: What is freezing of water?

Ans : Freezing is the process in which water turns to ice when cold enough (below 0°C temperature).

Q11: What is melting?

Ans : Melting is the process of turning a solid to a liquid.


Q12: Name the process by which water molecules continuously change to vapour.

Ans : Evaporation

Class 7 Science Chapter 5 Question Answers - Physical and Chemical Changes

Q13: At what temperature water evaporates?

Ans : 100 °C


Q14: Extraction of metal is a chemical process or physical process?

Ans : Chemical process


Q15: A medicine is the end product of the chain of ________________________.

Ans : Chemical reaction


Q16: Condensation of steam is chemical process or physical change?

Ans : physical change


Q17: Cutting of log of wood into pieces is a chemical process or physical change?

Ans : physical change


Q18: Name the two methods by which rusting of iron can be prevented.

Ans : By painting or greasing and by galvanizing with chromium or zinc


Q19: Give an example of chemical change in which heat, light, sound and unpleasant gases are produced.

Ans : Explosion of a firework


Q20: Define galvanisation.

Ans : The process of depositing a layer of zinc on iron is called galvanisation.

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FAQs on Class 7 Science Chapter 5 Question Answers - Physical and Chemical Changes

1. What is a physical change?$#

Ans. A physical change is a change in a substance that does not alter its chemical composition. Examples include changes in shape, size, or state of matter.

2. What is a chemical change?$#

Ans. A chemical change is a process that results in the formation of one or more new substances with different chemical properties. This can involve the breaking and forming of chemical bonds.

3. How can you differentiate between a physical and chemical change?$#

Ans. Physical changes are usually reversible and do not involve the formation of new substances, while chemical changes are often irreversible and result in the creation of new substances.

4. What are some examples of physical changes?$#

Ans. Examples of physical changes include melting ice, boiling water, crushing a can, and dissolving sugar in water.

5. What are some examples of chemical changes?$#

Ans. Examples of chemical changes include burning wood, rusting of iron, cooking an egg, and fermenting grapes to make wine.
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