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In a Nutshell
| NCERT Point | Simple Meaning |
|---|---|
| A physical change is one in which a substance or object undergoes a change in its physical properties and no new substance is formed. | Only appearance changes |
| A chemical change is one in which one or more new substances are formed. It involves a chemical reaction and can be represented by a chemical equation. | New substances form |
| Combustion, cooking, and rusting are examples of chemical changes. | Common chemical changes |
| Substances that undergo combustion are combustible substances. Heat and/or light are given out during combustion. | Burning produces energy |
| The lowest temperature at which a substance can catch fire is called its ignition temperature. | Minimum burning temperature |
| Some changes can be reversed and some cannot. | Changes vary reversibility |
| Some changes are desirable and some are not. | Changes have different values |
| Rocks undergo physical and chemical changes due to weathering to form soil. | Weathering creates soil |
| Erosion caused by flowing water and wind is a physical change. | Moving materials physically |
Quick Revision Table
| Term | Simple Meaning |
|---|---|
| Physical change | Only appearance changes |
| Chemical change | New substances form |
| Chemical reaction | Process forming new substances |
| Combustion | Burning with oxygen |
| Ignition temperature | Minimum burning temperature |
| Combustible substance | Can burn easily |
| Rusting | Iron becomes rust |
| Reversible change | Can get original back |
| Irreversible change | Cannot get original back |
| Desirable change | Useful helpful change |
| Undesirable change | Harmful unwanted change |
| Weathering | Rocks break into soil |
| Erosion | Moving soil particles |
| Bioluminescence | Light without heat |
