What is a Change?
A change is any difference between the initial and final state of a substance or object. Changes happen around us all the time.
Example:
Ice melts
Clothes dry
Bread is sliced
Fruits ripen
Plants grow
Types of Changes We Observe:
A change may occur in:
- Size – plant grows, pencil becomes shorter
- Shape – folding paper, moulding clay
- State – ice melts, water freezes, steam forms
- Colour – leaves turn yellow, banana ripens
- Smell – perfume spreads, flowers give fragrance
- Temperature – tea cools, soup heats
- Texture – dough softens, cotton becomes wet
- Sound – bell rings, paper tears
- Taste – lemon is sour, spoiled food tastes bad
Observing Changes – Five Senses:
We identify changes using our five senses.
| Sense Organ | Used to observe | Example |
|---|---|---|
| Eyes | Colour, size, shape | Yellow leaf |
| Ears | Sound | Bell ringing |
| Nose | Smell | Perfume |
| Tongue | Taste | Lemon |
| Skin | Temperature/Texture | Ice feels cold |
Physical Change:
A physical change is a change in which only the physical properties (shape, size, state or appearance) change. No new substance is formed.
Characteristics:
- No new substance is formed.
- Only shape, size or state changes.
- Usually reversible.
Example:
Ice \(\to\) Water
Water \(\to\) Steam
Folding paper
Cutting vegetables
Sharpening a pencil
Inflating a balloon
Chemical Change:
A chemical change is a change in which one or more new substances are formed with different properties.
Characteristics:
- New substance is formed.
- Usually irreversible.
- Heat, light, sound or smell may be produced.
- Colour may change.
- Gas or solid may be formed.
Example:
Rusting of iron
Burning paper
Cooking food
Curdling of milk
Baking a roti
Vinegar \(+\) Baking soda reaction
Physical Change vs Chemical Change:
| Physical Change | Chemical Change |
| No new substance is formed. | New substance is formed. |
| Only shape, size or state changes. | Composition changes. |
| Usually reversible. | Usually irreversible. |
| Example: Melting ice | Example: Rusting iron |