Changes Around Us: Physical and Chemical - Class 7 Science (CBSE)

Based on the 2026-27 Class 7 Science syllabus for the NCERT-aligned book Curiosity. Use these notes to understand, observe, explain, and answer in full sentences.

1. Why this chapter matters

Changes can be grouped by what happens to the substance. Some changes alter only form or state; others produce new substances with new properties.

This chapter is not meant for rote learning. Read every idea with an example, then ask: what can I observe, test, draw, measure, or explain?

2. Core ideas

Physical changes

A physical change usually changes shape, size, state, or appearance without forming a new substance. Melting ice and dissolving salt are common examples.

Chemical changes

A chemical change forms one or more new substances. Burning, rusting, curd formation, and reaction of vinegar with baking soda are examples.

Signs of chemical change

Colour change, gas formation, heat or light, smell, and precipitate formation can suggest a chemical change, but careful observation is needed.

3. Key points to remember

• Observation: Record what is actually seen, measured, or compared.
• Fair test: Change one factor and keep other factors the same.
• Conclusion: Use evidence to answer the question.
• Scientific vocabulary: Use precise terms from the chapter.

4. Worked examples

Example 1: Is tearing paper physical or chemical?

Tearing changes size and shape but no new substance forms, so it is a physical change.

Example 2: Why is burning paper a chemical change?

New substances such as ash and gases form, and the original paper cannot be recovered.

Example 3: What happens when vinegar reacts with baking soda?

A gas is produced, showing a chemical reaction.

Example 4: Why is crystallisation useful?

It helps separate and purify a solid from solution.

5. Activity and observation

Make a two-column observation table. Classify melting wax, cutting fruit, rusting iron, burning magnesium, dissolving sugar, and curd setting as physical or chemical, with reasons.

Write the activity in this format:

• Aim: What are you trying to find out?
• Materials: What did you use?
• Procedure: What steps did you follow?
• Observation: What did you see or measure?
• Conclusion: What scientific idea does it prove?

6. Common mistakes

• Writing only definitions without examples.
• Drawing diagrams without labels.
• Confusing observation with conclusion.
• Ignoring units in speed, time, distance, temperature, or measurement questions.
• Giving unsafe suggestions for experiments instead of classroom-safe methods.

7. Practice set

1. Define the main idea of Changes Around Us: Physical and Chemical.
2. Write two key terms from this chapter and explain them.
3. Describe one activity that proves an idea from this chapter.
4. Give one real-life application of physical change.
5. Write one difference-based question from this chapter.
6. How can you make your answer more scientific?

8. Answer key

1. Define the main idea of Changes Around Us: Physical and Chemical. Answer: Changes can be grouped by what happens to the substance. Some changes alter only form or state; others produce new substances with new properties.

2. Write two key terms from this chapter and explain them. Answer: physical change and chemical change are central terms. Define each with one example from daily life.

3. Describe one activity that proves an idea from this chapter. Answer: Make a two-column observation table. Classify melting wax, cutting fruit, rusting iron, burning magnesium, dissolving sugar, and curd setting as physical or chemical, with reasons.

4. Give one real-life application of physical change. Answer: Use the chapter idea to explain a daily event, then name the observation that supports your answer.

5. Write one difference-based question from this chapter. Answer: Compare two related ideas, such as Physical changes and Chemical changes, using meaning and example.

6. How can you make your answer more scientific? Answer: Use observation, correct vocabulary, labelled diagrams or tables, and a clear reason.

9. Quick revision

• Main themes: physical change, chemical change, reversibility, new substance, crystallisation.
• Learn definitions with examples.
• Practise one diagram, table, or activity.
• Revise the worked examples.
• Write answers using cause, evidence, and conclusion.