Contrast irreversible with reversible visually, reusing last lesson's arrow motif.
The one-way arrow
Where reversible change had a two-way arrow (⇔), irreversible change gets a bold one-way arrow (→) with a "no return" sign over the backward path. Students draw the reactants, the one-way arrow, and the new substance — the broken-return arrow is the visual signature of irreversible change.
Four-signs icon panel
Give the four signs of chemical change a fixed icon set (bubbles = gas, palette = colour change, flame = heat/light, star = new material). Students stamp the matching icons onto each observation, building a visual record of why they classified a change as irreversible.