Boxi Learn › Chemistry › Stage 3 · Structure and Evidence
New stuff, or the same stuff changed?
CHEM-1 Atoms are rearranged, never lostX-2 Evidence outweighs opinion
What many people think
Bubbles, a colour change or a substance vanishing always mean a chemical reaction, so boiling and dissolving are chemical changes.
The idea
A change is chemical only when a new substance forms; melting, boiling and dissolving keep the same molecules, burning makes new ones.
Explain it
A friend says: “The sugar disappeared in my tea, so dissolving is a chemical change.” What evidence would you show them?
Try at home
Stir a teaspoon of sugar into a little water and leave it on a saucer for a few days. What is left when the water has gone? Could you get baking soda back after pouring vinegar on it?