--- title: "Reversible and irreversible changes: freezer vs oven" description: "A 40-minute lesson on reversible and irreversible changes: freeze and bake on the whiteboard, then melt chocolate for real. Fits Year 5 and NGSS 2-PS1-4." source_name: "Game Tailors" source_url: "https://extreemtekenen.nl/en/for-teachers/reversible-changes/" site_home: "https://extreemtekenen.nl/" source_description: "The drawing app where the paper is real. No ads, no accounts, no data collected." locale: "en" legal: - "Game Tailors · Schieweg 15Y-40, 2627 AN Delft (NL)" - "KvK 92437702 · VAT NL866044474B01" - "info@gametailors.com · +31 6 4227 5919" copyright: "© 2026 Game Tailors" published_at: "2026-10-24T00:48:09.071Z" modified_at: "2026-10-24T01:17:53.378Z" --- # Reversible and irreversible changes: freezer vs oven ## Can you melt it back? A reversible change can be undone: melted chocolate sets again and frozen paint thaws. An irreversible change makes something new that won't go back, like a cooked egg, caramel or burnt paper. In 40 minutes pupils predict, test it with the freezer and the oven on the whiteboard, then melt chocolate for real. [Play in your browser]()[Jump to the lesson plan](<#plan>) - 40 minutes - Year 5 · Grade 2 - Free tools only ![Painted illustration of two sheets of paper, one covered in frost ferns from the freezer and one baked golden from the oven, the painter holding an ice cube and an oven glove.]() ## At a glance Age 7 to 10 \(England Year 5; US grade 2; NL groep 5 to 7\) Fits KS2 Year 5 properties and changes of materials · NGSS 2-PS1-4 · kerndoel 42 Time 40 minutes In the app \(all free\) Ice cream, Chocolate, Egg, Ice cube, Iron, Bake in the oven, Put in the freezer, Undo For real Chocolate, small zip bags, bowls of warm water, ice cubes, bread and a slice of toast, a raw and a hard-boiled egg On screen only Burning \(the Fire tool\), as an example of an irreversible change ## Learning objective and standards **Objective:** pupils can sort everyday changes into ones that can be reversed and ones that can't, and give evidence for their choice. **Success criteria** - I can predict whether a change can be undone. - I can test my prediction and say what I saw. - I can explain that some changes make a new material that won't turn back. [NGSS 2-PS1-4]()[England science programmes of study]() ### Where it fits - **England, Year 5, Properties and changes of materials:** changes of state are reversible; some changes form new materials and are not usually reversible, including burning. - **NGSS 2-PS1-4:** construct an argument with evidence that some changes caused by heating or cooling can be reversed and some cannot. - **Netherlands, kerndoel 42:** investigating materials and physical phenomena such as temperature. - **Flanders:** the minimumdoelen *wetenschap en techniek* on materials and their changes. ![Painted illustration of two sheets of paper, one covered in frost ferns from the freezer and one baked golden from the oven, the painter holding an ice cube and an oven glove.]() ## What the app shows Everything for this lesson is in the free part of the app. - **Put in the freezer** gives the page three hours in a freezer. Everything with water in it freezes solid: puddles, paint, sauces, and ice cream goes rock hard again. Wax, eggshell and caramel don't freeze, because there's no water in them. Then it thaws back within a minute or so: thin films first, thick lumps last. - **Chocolate** melts glossy and runny when it's warmed \(hold the **Iron** over it\) and sets hard again about 20 seconds after the heat goes. - **Bake in the oven** gives the page twenty minutes at 180 °C. Egg white sets white with crisp brown edges, honey and ice cream cook down to caramel, and the paper toasts brown at its edges. None of that comes back when it cools. - **Fire** burns the paper into holes. That one stays on the screen. One thing to point out: the app has an **Undo** button, and it will put a baked page back. Real life has no undo button. That's the whole difference between the two kinds of change. [Play in your browser]() ## The lesson, step by step Set up before the lesson: the browser version open on the board, a fresh sheet of paper, and the real materials on a tray per group. Boil one egg beforehand. 1. 5 minutesHook: an ice cream on the boardDrop an **Ice cream** scoop on the paper and let the class watch it slump into a puddle \(a scoop takes about a minute and a half\). Ask: *can we get our ice cream back?* 2. 5 minutesPredictShow four things on the board: the melted ice cream, a bar of **Chocolate**, an **Egg** and the bare paper. For each, pupils predict in pairs: freezer or oven, and will it go back afterwards? Record the guesses in a two-column table: *goes back* / *doesn't go back*. 3. 10 minutesTry it on the boardTap **Put in the freezer**: the puddle goes hard, and then thaws again. Melt the chocolate with the **Iron**, take the iron away and count to twenty: it sets. Then tap **Bake in the oven**: the egg white turns white, the ice cream becomes caramel, the paper browns. Wait for it to cool. Does anything turn back? Let a pupil press **Undo** and ask why real life can't. 4. 15 minutesDo it for realIn groups: put a few squares of chocolate in a zip bag and hold it in a bowl of warm water until it melts, then lay it flat on a cool surface and watch it set. Put an ice cube on a saucer and watch it melt. Then compare a slice of bread with a slice of toast, and a raw egg with the hard-boiled one: can anyone turn them back? 5. 5 minutesExplainBack to the table of predictions. Which were right? Draw out the rule: melting and freezing change the *state* and can go back; cooking and burning make a *new material* that can't. Exit question: *is a burnt match reversible?* Safety - Use warm tap water, not boiling water; an adult fills the bowls. - An adult boils the egg and makes the toast before the lesson. - Check allergies before using chocolate \(milk, soya, nuts\); use a free-from bar where needed. Follow your school's rules on eating in science. - Burning is shown **on the screen only**. No matches, candles or lighters in this lesson. - Wipe up meltwater straight away so nobody slips. ## Vocabulary and differentiation **Key words** - **reversible change**: a change that can be undone - **irreversible change**: a change that can't be undone, usually because a new material forms - **melt / freeze**: solid to liquid, liquid to solid - **set / solidify**: a liquid turning solid as it cools - **thaw**: frozen things warming and melting - **state**: solid, liquid or gas - **new material**: something that wasn't there before, like caramel or ash Support ### Sort, don't write Give picture cards \(ice cube, chocolate, egg, toast, ash\) to sort into two hoops. Younger pupils \(grade 2\) can stop here: that's the NGSS argument with evidence. Core ### Predict and record Use the two-column table, with one sentence of evidence for each item: *I saw…, so I think…* Stretch ### Is it really the same? Melted ice cream refrozen for real comes out icy, not creamy. Is that still a reversible change? And why can the oven at 180 °C toast paper without setting it alight, when the Fire tool burns it? \(Paper lights at about 230 °C.\) What is the difference between a reversible and an irreversible change? A reversible change can be undone, like melting chocolate and letting it set again. An irreversible change makes a new material that can't easily turn back, like cooking an egg or burning paper. Is melting chocolate a reversible change? Yes. Melting changes chocolate from solid to liquid, and it sets solid again as it cools. If it's heated too much it can burn, and burning isn't reversible. Is cooking an egg reversible? No. Heat changes the proteins in the egg white so it turns from clear to white and firm, and cooling it doesn't change it back. Is freezing water reversible? Yes. Ice melts back into water when it warms up, and the water can be frozen again. Do pupils need accounts to use the app in class? No. Open play.extremedrawing.com in the browser; nobody logs in and no data is collected. ## Next lessons and experiments ![Painted illustration of the painter pointing a pencil at a melting ice cube, beside melting chocolate and a kettle letting off steam.]() ### [States of matter]() Solids, liquids and gases with ice cream, chocolate and steam. ![Painted illustration of the painter pointing at a golden-brown heart and star that appeared on paper after ironing, with an iron, half a lemon and a cotton bud.]() ### [Invisible ink]() Lemon juice writing that heat turns brown for good: an irreversible change. ![Painted illustration of the painter pouring red vinegar onto a heap of baking soda on a tray, which fizzes up into pink foam.]() ### [Baking soda and vinegar]() The acid and bicarbonate of soda reaction named in the Year 5 curriculum. ## Freeze it, bake it, then do it for real Free in the browser, no pupil accounts. More lessons and the curriculum map are on the teachers' page. 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