Reversible & irreversible changes

Dissolving, mixing, burning, rusting, and separating mixtures

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Try each question. If you're stuck, leave it and come back. The answer key is on the last page.

1
True or false? Melting ice is a reversible change because you can freeze it again. A) True B) False
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2
True or false? Burning wood is a reversible change. A) True B) False
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3
Which separation method would you use to get clean water from muddy water? A) Filtering B) Burning C) Magnetism D) Sieving
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4
Complete the sentence about dissolving. When sugar dissolves in water, the sugar seems to disappear but it has not gone - this is a ___ change because you can get the sugar back by evaporating the water.
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5
Sort these steps for separating sand from salt water in the correct order. Put these in order: Collect the salt left behind, Filter the mixture to remove sand, Heat the salt water to evaporate the water, Mix sand and salt in water
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6
What new substance is formed when iron rusts? A) Iron oxide B) Carbon dioxide C) Salt D) Pure iron
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7
Sort these changes into the correct category: put reversible changes first, then irreversible changes. Put these in order: Burning paper, Melting chocolate, Cooking an egg, Dissolving salt
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8
A chef heats sugar gently and it melts. Then she heats it strongly and it turns black and gives off smoke. Which statement is correct? A) Gentle heating was reversible but strong heating caused an irreversible change B) Both are reversible changes C) Both are irreversible changes D) Gentle heating was irreversible but strong heating was reversible
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9
Complete the sentence about irreversible changes. When a candle burns, the wax reacts with ___ from the air to produce carbon dioxide and water vapour.
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10
True or false? Burning a candle is a reversible change. A) True B) False
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Answer key

Reversible & irreversible changes · for parents and teachers

1
True
Melting ice is reversible - you can freeze the water back into ice. No new substance is formed; it is still water (H2O) in a different state.
2
False
Burning is irreversible - new substances (ash, carbon dioxide, water vapour) are formed that cannot be turned back into the original wood.
3
Filtering
Filtering uses filter paper with tiny holes that let water through but trap solid mud particles. Sieving has holes too large for fine particles.
4
reversible
Dissolving is reversible because no new substance is formed. The sugar is still there in the water and can be recovered by evaporation.
5
Mix sand and salt in water, Filter the mixture to remove sand, Heat the salt water to evaporate the water, Collect the salt left behind
Dissolving the salt separates it from sand. Filtering removes insoluble sand. Evaporating removes water, leaving salt crystals behind.
6
Iron oxide
Rusting is an irreversible chemical change. Iron reacts with oxygen and water to form iron oxide (rust), which is a completely different substance.
7
Melting chocolate, Dissolving salt, Burning paper, Cooking an egg
Melting and dissolving are reversible (no new substance). Burning and cooking are irreversible - new substances form that cannot be changed back.
8
Gentle heating was reversible but strong heating caused an irreversible change
Gentle heating melts sugar (reversible - it can solidify again). Strong heating burns it, creating carbon (black) and smoke - new substances that cannot become sugar again.
9
oxygen
Burning (combustion) is a chemical reaction between a fuel and oxygen. The wax reacts with oxygen to produce carbon dioxide and water vapour - this is irreversible.
10
False
False. Burning is irreversible. New substances like carbon dioxide and water vapour are formed.