Run these five changes in order. Students work silently, completing their results grid as you go. This task aligns to the Observing chemical change assessment, so give thinking time after each demonstration.
| # | Change & what to highlight | Answer (with reason) | Safety |
|---|---|---|---|
| 1 | Melting butter on a warm plate — point out the solid turning to clear liquid. | Reversible — same substance; cooling makes it solid again. | Warm plate only; use a heat mat. |
| 2 | Toasting bread — note the colour change and the smell. | Irreversible — new substance (you can't un-toast it). | Hot toaster; teacher only. |
| 3 | Popping popcorn — the kernel bursts as water inside turns to steam. | Irreversible — the kernel can't go back. | Hot popper and steam; keep students back. |
| 4 | Ice melt then refreeze — melt a cube, then return it to the freezer. | Reversible — still H₂O the whole time. | Low risk. |
| 5 | Burning paper (small, in a tray) — ash, smoke and heat. | Irreversible — new substances: ash, smoke, gas. | Open flame; tray, fire blanket nearby, ventilate. |