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🧪 Physical and Chemical Changes

Melt it, burn it, rust it, fizz it: learn the one question that tells a physical change from a chemical one.

lessons

~20 min

to learn

🔬 Science

subject

Teens

level

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What you’ll learn

Physical ChangesUnderstand that a physical change makes no new substance and is usually reversible, using melting, changing state, and dissolving as examples.A physical change alters how a substance looks or its state, but no new substance is made. Melting, freezing, boiling, and dissolving are all physical changes, and they can usually be reversed. Water stays water whether it is ice, liquid, or steam.
Chemical ChangesUnderstand that a chemical change forms new substances, is usually hard to reverse, and can be spotted through signs like colour change, gas, and heat or light.A chemical change, or chemical reaction, forms one or more new substances with different properties, and it is usually hard to reverse. Burning wood, mixing baking soda with vinegar, and rusting are examples. Signs of a chemical change include a colour change, bubbles of gas, heat or light, and a new smell.
Telling Them ApartUse the test 'has a new substance been made?' to classify everyday changes as physical or chemical.To tell the two apart, ask whether a new substance has formed. If not, it is a physical change and usually reversible, like melting or dissolving. If a new substance appears, it is a chemical change and usually hard to reverse, like burning, rusting, or cooking an egg.

Questions this course answers

What happens to the substance during a physical change?

In a physical change only the shape or state alters, so no new substance is formed.

Why is melting ice a good example of a physical change?

Physical changes are usually reversible, and freezing turns the water straight back into ice.

What must happen for a change to be a chemical change?

A chemical change always forms one or more new substances with different properties.

Which of these is a sign that a chemical change is happening?

Bubbles of gas are a classic sign that a new substance is being made in a reaction.

Why is burning wood a chemical change?

Burning turns wood into new substances such as ash, smoke, and gases, which is a chemical change.

Iron turning to rust in damp air is which kind of change?

Rust is a new substance formed when iron reacts with oxygen and water, so rusting is a chemical change.

Grounded in trusted sources

Royal Society of Chemistry
BBC Bitesize
Britannica

Every Wunder lesson is built from real, reputable sources — never invented.

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