The67Sprint — LearningMap: Changes Around Us: Physical and Chemical

🔄 Physical Changes

A change where no new substance is formed — only shape, size, state or colour alters
Most are reversible (melting ice, dissolving sugar) but some are irreversible (tearing paper, breaking glass, cutting wood)
Very little or no energy is absorbed or given out during a physical change
Activity 5.1 examples: adding beetroot extract to water, folding paper, crushing chalk
Boiling water to form steam is a physical change — the water is still chemically H₂O

⚗️ Chemical Changes

A permanent change where one or more entirely new substances are formed
Usually accompanied by production or absorption of heat, light or sound
Indicators: change in colour or smell, gas evolved, precipitate formed, sound produced
Examples: burning wood, rusting of iron, curdling of milk, popcorn from corn (Activity 5.1)
Word equation: Vinegar + Baking soda → Carbon dioxide + other substances

Curdling 🥛 Popcorn 🍿

🔩 Rusting & Combustion

Rusting needs both oxygen AND water (moisture) present together — iron does not rust in water alone
Rust (iron oxide) can be prevented by painting, greasing, oiling, alloying, or galvanization (zinc coating)
Combustion needs three things together: fuel, oxygen, and heat reaching the ignition temperature
Ignition temperature is the minimum temperature at which a substance catches fire

Memory Cheat Code

Rust Needs Two — Iron + Oxygen + Water, together, at the same time. Remove either oxygen or water and rusting stops.

Quick Recall — Sprint Facts

No New Substance Physical change — only shape, size, state or colour alters

New Substance Formed Chemical change — permanent, often irreversible

Fe + O₂ + H₂O Rusting needs oxygen and moisture together

Zinc Coating Galvanization protects iron from rusting

CaCO₃ Forms CO₂ passed through lime water turns it milky

Cold Light Bioluminescence — light without heat, in fireflies

🔑 Key Terms

Ignition Temperature

The minimum temperature at which a substance catches fire and starts burning

Galvanization

Coating iron with a protective layer of zinc to keep out air and moisture

Crystallization

A physical process used to obtain large, pure crystals of a substance from its solution

Weathering

Physical and chemical breakdown of rocks into soil over time

Erosion

Physical transport of broken rock sediments by wind or water to a new location

Bioluminescence

A chemical reaction in living organisms, like fireflies, that produces light without heat

🏆 Olympiad & Challenger Edge

Atomic Bonds Breaking

At the microscopic level, a chemical change happens because the internal bonds holding atoms together break and reform in a new arrangement, creating a substance with different properties.

The Fire Triangle

Combustion is formally modelled as a triangle of Fuel, Oxygen and Heat — remove any one side of the triangle and the fire cannot survive.

Cold Light Chemistry

Fireflies perform a special chemical reaction called bioluminescence that releases light energy without releasing heat energy — unlike combustion.

Displacement Reaction

Dipping an iron nail into blue copper sulphate solution turns the solution green (iron sulphate forms) and leaves a brown copper deposit on the nail — proof of a chemical change.

All Physical Changes Are Reversible?

Wrong. Tearing paper, cutting wood, or grinding wheat are physical changes, yet they cannot be undone.

Boiling Water Is Chemical?

No. Steam is still H₂O — only the state changed from liquid to gas. No new substance formed.

Iron Rusts in Water Alone?

Incorrect. Rusting strictly needs both oxygen and water present at the same time.

Weathering = Erosion?

No. Weathering breaks rocks down into soil; erosion is the separate process of transporting those sediments.

Idlis & Chapatis

Rolling dough into chapatis is physical; fermenting batter into idlis is a chemical change that cannot be reversed.

Rusty Bicycle Chains

A chain left in the rain rusts from oxygen and moisture together — greasing it blocks both and prevents rust.

Galvanized Ships & Bridges

Ships and bridges exposed to salty air are painted and galvanized with zinc to stop rusting.

Digesting Your Food

Chewing breaks food apart physically; acids and enzymes in the stomach then change it chemically.

Irreversible ≠ Chemical

Breaking glass is physical and irreversible — the substance (glass) hasn't changed, only its shape has.

The Candle Trap

Melting wax is physical; the wick burning wax vapour into light, heat and CO₂ is chemical — both happen at once.

Fire Needs All Three

Remove fuel, oxygen or heat and combustion stops — a blanket smothers fire by cutting off oxygen.

Lime Water Turns Milky

CO₂ passed through lime water forms insoluble calcium carbonate — a chemical change, not a colour trick.

Logic Chain

Step 1

A candle is lit and the solid wax near the flame begins to melt into a liquid

Step 2

The liquid wax travels up the wick and turns into wax vapour from the heat

Step 3

The wax vapour reacts with oxygen in the flame and burns, releasing heat and light

Step 4

Carbon dioxide and water vapour are given off as new substances — a chemical change is complete

🦉

Mentor Byte

"Whenever you're unsure if a change is physical or chemical, ask the golden question: did the substance's identity change, or just its outfit? Tear paper and it's still paper — smaller, but the same substance. Burn paper and it becomes ash and smoke, with an entirely new identity. Keep a close eye on the candle question too — examiners love testing whether you notice that physical and chemical changes can happen in the very same event."

💛 Parent Tip

Next time you make lemonade together, point out that dissolving the sugar is reversible and physical, but ask your child what happens when milk turns into curd overnight — a chemical change they can taste but never undo.