NCERT Solutions for Class 7 Science Chapter 6
Important NCERT Questions
7th Chapter 6 Physical and Chemical Changes
NCERT Books for Session 2022-2023
CBSE Board and State Board
Questions No: 7
Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.
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Burning of wood is a chemical change because wood on burning converted to new substances like ash (carbon), carbon dioxide gas, water vapour, heat and light. The change is irreversible.
While cutting of wood in smaller pieces is a physical change because the original composition of wood does not change. No new substances are formed.
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The burning of wood and cutting it into small pieces are categorized as distinct types of changes owing to their unique characteristics:
1. Burning of Wood (Chemical Change):
– Chemical Transformation: When wood undergoes combustion, it experiences a chemical change. The wood reacts with oxygen, resulting in the release of heat, light, and the formation of new substances like carbon dioxide, water vapor, and ash.
– Altered Composition: Combustion transforms the chemical composition of wood, breaking down its organic matter into different compounds.
2. Cutting Wood into Small Pieces (Physical Change):
– Physical Modification: Cutting wood represents a physical change. The wood’s original substance remains unchanged, but its physical structure is modified.
– Unchanged Composition: Despite altering the wood’s size and shape, cutting does not alter its chemical composition or inherent properties.
Distinctive Factors:
– Nature of Change: Burning initiates a chemical transformation, altering wood’s composition, while cutting signifies a physical alteration, reshaping wood without changing its chemical identity.
– Resultant Outcomes: Burning wood leads to the formation of new substances (like ash and gases), whereas cutting produces smaller wood pieces without altering their basic chemical structure.
In essence, burning wood and cutting it into smaller pieces are differentiated by their dissimilarities: burning as a chemical change modifies wood’s composition, while cutting represents a physical change, modifying its structure without affecting its chemical properties.