This is an assessed observation task, so the demonstrations and the grid stay fixed. Vary how students stay physically engaged and prepare — not what is assessed.
Active observation stance
Between each demonstration, give a brief physical "reset" — students mime the change they just saw (hands packing tight then spreading for melting; a sudden "poof" for popcorn). The gesture encodes the observation kinesthetically before they write it in the grid.
Warm-up sign sort
As a pre-task warm-up (not assessed), students physically sort a set of everyday-change cards into reversible/irreversible piles to re-activate the prior two lessons, then clear them away before the task begins.