Your teacher is holding up an ice cube and a square of chocolate. What do you think will happen if we warm them gently? And once they have changed, can we ever get them back the way they were?

Watch what happens when I melt a little ice at the front. Which do you think melting ice is: reversible or irreversible?

We will warm ice and chocolate in a gentle warm-water bath. Before anything goes in the water, open your Investigation Journal page. Write one prediction for ice and one for chocolate: will each melt, and can we get the solid back again? Talk with your group, then be ready to share one prediction.

Work through these beats with your group:

1. Set up. Put one ice cube in one small dish and one square of chocolate in the other. Stand both dishes carefully in the warm-water tray.
2. Watch and record. Hands off the ice, chocolate and melt liquid. No tasting. Write quick observations on your Investigation Journal page: which melts first, solid or liquid, clear or brown, soft or runny.
3. Choose your focus. As a group, decide and write on your journal: how will you judge "melted enough"?
4. Pick your reverse check. Which will you trust more: ice, judged from what we already know about freezing, or chocolate, judged from the cool-back clues? Write that too.
5. Cool-back check. When your teacher says, lift the chocolate dish onto a cool saucer and watch for one to two minutes. Look for clues that it is beginning to firm or solidify again.
6. Decide. Is each change reversible or irreversible so far? Ice reverse is judged from known freezing (we are not freezing the melt water in class). For chocolate, use the cool-back clues you saw.

Before the toaster starts, write one prediction on your Investigation Journal page: what will happen to the bread, and could we ever turn it back into soft white bread? Then watch the demonstration carefully.