Chemical vs Physical Changes
Grade 5 · Science · Study Guide
Explore the difference between physical changes that alter form and chemical changes that create entirely new substances.
Matter can undergo two main types of changes: physical and chemical. A physical change alters the size, shape, or state of matter but does NOT create a new substance. Cutting paper, melting ice, and dissolving sugar in water are all physical changes because the original material is still present — just in a different form.
A chemical change, on the other hand, produces one or more new substances with different properties than the original. Signs that a chemical change has occurred include: producing a gas (bubbling), a color change, forming a solid from liquids (precipitate), releasing heat or light, or producing a smell.
Burning wood is a chemical change — the wood turns into ash, smoke, and carbon dioxide, which are completely different from the original wood. Rusting iron is also a chemical change because iron reacts with oxygen and water to form iron oxide (rust).
One helpful test: can you easily reverse it? Physical changes are usually reversible (melting ice can refreeze), while chemical changes are typically irreversible (you cannot un-bake a cake). However, reversibility alone is not a perfect rule — always look for evidence of new substance formation.
Key terms
- Physical Change
- A change in the size, shape, or state of matter that does NOT produce a new substance.
- Chemical Change
- A change that produces one or more new substances with different properties from the original.
- Precipitate
- A solid that forms from two mixed liquids during a chemical reaction.
- Reactant
- A starting substance that enters into a chemical reaction.
- Product
- A new substance formed as a result of a chemical reaction.
- Reversible Change
- A change that can be undone to recover the original substance, common in physical changes.
Flashcards
- Melting ice
- Physical change — water molecules spread apart but H2O is still H2O.
- Burning wood
- Chemical change — produces ash, CO2, and smoke; new substances formed.
- Rusting iron
- Chemical change — iron + oxygen + water → iron oxide (rust).
- Cutting paper
- Physical change — shape changes but paper is still paper.
- Baking a cake
- Chemical change — heat causes ingredients to react and form new substances.
- Dissolving sugar
- Physical change — sugar molecules spread through water but can be recovered by evaporation.
- Gas bubbles forming
- A sign of chemical change — a new gaseous substance is being produced.
Questions
Which of the following is a chemical change?
- Cutting a piece of paper
- Melting butter on toast
- Burning a candle
- Crushing an aluminum can
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Answer: Burning a candle
Burning a candle is a chemical change because the wax reacts with oxygen to produce new substances: carbon dioxide, water vapor, and soot.
Dissolving salt in water is a chemical change because the salt disappears.
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Answer: False
Dissolving salt is a physical change. The salt molecules spread through the water but no new substance is created — you can recover the salt by evaporating the water.
When iron reacts with oxygen and water to form rust, this is an example of a ________ change.
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Answer: chemical
Rusting is a chemical change because iron reacts with oxygen and water to form iron oxide (rust), a completely new substance.
Which sign most strongly indicates a chemical change has occurred?
- The substance changes shape
- A new gas is produced and a color change occurs
- The substance melts
- The substance is cut into smaller pieces
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Answer: A new gas is produced and a color change occurs
Producing a new gas and a color change are both strong indicators that new substances have formed, which is the hallmark of a chemical change.
Physical changes are usually reversible, while chemical changes are typically not.
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Answer: True
Physical changes like melting or dissolving can generally be reversed (refreeze, evaporate). Chemical changes like burning or rusting produce new substances that cannot easily revert.
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