Welcome to Bodhiclasses, where learning meets clarity and curiosity. Our aim is to help every student grasp complex scientific concepts with ease, using real-life examples and insightful analysis. Today, we explore Chapter 5 – Changes Around Us from the NCERT Class 7 Science textbook. This chapter is all about understanding the changes around us, transformations that materials undergo in our daily lives — and classifying them meaningfully.
This chapter answers one fundamental question: How and why do substances change? It helps students distinguish physical changes around us from chemical changes, and introduces them to the concept of combustion, reversible/irreversible changes, and desirable/undesirable transformations in nature and everyday life.
🧪 Key Concepts Explained
1. Physical Changes Around Us
These are changes that affect only the form, shape, or state of a substance — no new substance is formed.
📌 Examples:
- Melting of ice
- Folding paper
- Chopping vegetables
- Dissolving sugar in water
Such changes are usually reversible, meaning the original substance can be recovered.
2. Chemical Changes Around Us
These are changes where new substances are formed with different properties. These changes are irreversible in most cases and involve chemical reactions.
📌 Examples:
- Rusting of iron
- Curdling of milk
- Burning of a magnesium ribbon
- Reaction of vinegar with baking soda
Chemical changes often involve production of gas, heat, light, or a new solid (precipitate).
3. Combustion and the Fire Triangle
The chapter introduces combustion as a chemical change where a substance reacts with oxygen to produce heat and/or light.
✅ Three conditions needed for combustion:
- Fuel (a combustible substance)
- Oxygen
- Heat (to reach ignition temperature)
The idea of the fire triangle helps students understand how fire starts and can be controlled.
4. Reversible and Irreversible Changes Around Us
Students learn how to identify if a change can be undone.
🟢 Reversible: Melting wax, folding paper, boiling water
🔴 Irreversible: Rusting, making popcorn, burning wood
This helps build critical thinking around transformation processes in nature and industry.
5. Desirable and Undesirable Changes Around Us
Not all changes are beneficial.
✅ Desirable: Cooking food, composting, ripening of fruits
🚫 Undesirable: Food spoilage, rusting, air pollution due to combustion
Students are encouraged to reflect on human impact and environmental responsibility.
6. Natural Physical and Chemical Changes
🌍 Weathering: Breaking of rocks into soil through temperature, water, and roots (can be physical or chemical)
💨 Erosion: Movement of soil and rock by wind or water (a physical change)
These slow, natural changes shape our planet over thousands of years.
🧠 Learning Outcomes
After studying this chapter, students will be able to:
- Differentiate between physical and chemical changes
- Understand chemical reactions and their signs
- Explain the requirements for combustion
- Recognize reversible and irreversible changes
- Identify desirable vs undesirable changes
- Appreciate natural processes like weathering and erosion
🌱 Real-Life Applications
- Testing for carbon dioxide using lime water (as in fire safety or baking)
- Understanding why iron rusts and how to prevent it
- Recognizing safety measures during fires
- Exploring how soil forms and why landslides occur
These insights bridge classroom knowledge with the real world.
🧑🔬 Activities and Experiments
This chapter includes interactive experiments like:
- Blowing air through lime water to test for CO₂
- Observing vinegar-baking soda reaction
- Burning a candle to identify both physical and chemical changes
- Focusing sunlight using a magnifying glass to find ignition temperature
These help students observe science in action — fostering enquiry and curiosity.
👩🎓 Tips for Students
- Always ask: “Is a new substance formed?”
- Observe: Is the change reversible? Does it give off heat, light, or gas?
- Practice with real-life examples – in the kitchen, garden, and outdoors
- Try drawing the fire triangle and identifying fuel-oxygen-heat in any combustion scenario
📚 Chapter Highlights
| Concept | Type of Change | Reversible? | Example |
|---|---|---|---|
| Melting Ice | Physical | Yes | Solid water to liquid |
| Rusting of Iron | Chemical | No | Iron + air + water → Rust |
| Burning Candle (wax melts & burns) | Both Physical & Chemical | Partly | Wax melts (physical), vapour burns (chemical) |
| Folding Paper | Physical | Yes | Change in shape only |
| Curdling of Milk | Chemical | No | Formation of lactic acid |
🔚 Conclusion
Chapter 5 of Class 7 Science beautifully blends observation, experimentation, and reasoning to help learners understand how our world is constantly changing — sometimes visibly, sometimes chemically. It sets a strong foundation for concepts that will be explored in greater depth in higher classes.
Let the world around you become your laboratory — notice every drop of dew, every rusted nail, and every puff of gas from a reaction. Science is not just in books; it is all around us.
