What is Physical and Chemical Changes Class 7: Complete Guide
By ConceptScroll Team · Published on 19 June 2026 · 3 min read
In Class 7 Science, understanding what is Physical and Chemical Changes is essential. Physical changes alter the appearance without changing the substance, while chemical changes create new substances. This chapter from the NCERT syllabus explains these concepts with examples and comparisons.
Definition of Physical and Chemical Changes
Physical changes are changes in the state or appearance of a substance without altering its chemical composition. For example, melting ice changes its state from solid to liquid but remains water.
Chemical changes involve the formation of one or more new substances with different properties. For example, burning paper produces ash and gases, which are different from the original paper.
Both types of changes are part of everyday life and important to understand in Class 7 Science.
Characteristics of Physical Changes
Physical changes have these key features:
- No new substance is formed
- Usually reversible (e.g., freezing and melting)
- Change in size, shape, or state
- Examples include tearing paper, dissolving sugar in water, and boiling water
Physical changes only affect physical properties like texture, shape, or phase but not chemical properties.
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Characteristics of Chemical Changes
Chemical changes show these characteristics:
- New substances with different properties are formed
- Usually irreversible
- Energy changes occur (heat, light, sound)
- Examples include burning wood, rusting iron, and cooking food
Chemical changes involve breaking and forming chemical bonds, changing the substance’s identity.
Comparing Physical and Chemical Changes
Here is a comparison table to help you understand the differences:
| Feature | Physical Change | Chemical Change |
|---|---|---|
| Substance formed | No new substance | New substances formed |
| Reversibility | Usually reversible | Usually irreversible |
| Energy change | Minor or none | Often involves energy change |
| Examples | Melting, freezing, tearing | Burning, rusting, cooking |
This table helps Class 7 students quickly spot the main differences.
Examples and Practical Applications
Understanding examples helps clarify these concepts:
- Physical change example: Ice melting to water. The formula for melting is not chemical but physical.
- Chemical change example: Burning methane gas. The chemical reaction is:
$$ CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O + energy $$
This reaction produces new substances (carbon dioxide and water) and releases energy.
Knowing these examples helps students identify changes in daily life and exams.
How to Identify Physical and Chemical Changes
To identify the type of change, ask these questions:
- Is a new substance formed? If yes, it’s chemical.
- Can the change be reversed easily? If yes, it’s physical.
- Is there a change in energy (heat, light)? Chemical changes often show this.
Example: When sugar dissolves in water, it’s a physical change because no new substance forms and it can be recovered by evaporation.
Example: When iron rusts, it’s a chemical change because rust is a new substance formed.
Frequently asked questions
What is a physical change in Class 7 Science?
A physical change alters the appearance or state without forming a new substance, like melting ice.
How is a chemical change different from a physical change?
Chemical change forms new substances with different properties, while physical change does not.
Can physical changes be reversed easily?
Yes, most physical changes are reversible, such as freezing and melting.
Give an example of a chemical change from daily life.
Burning wood is a chemical change because it produces ash and gases.
Why is burning considered a chemical change?
Because it produces new substances and releases energy, changing the original material.
Is dissolving sugar in water a physical or chemical change?
It is a physical change because sugar can be recovered and no new substance forms.
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