Folding paper, inflating a balloon, crushing chalk — only shape, size, or state changes. No new substance forms.
Blowing breath into lime water turns it milky — a genuinely new substance, calcium carbonate, has formed.
Turning milky confirms carbon dioxide gas is present.
Mixing them fizzes as carbon dioxide gas escapes.
A substance reacts with oxygen, releasing heat and often light.
The minimum temperature to catch fire — seen when a magnifying glass focuses sunlight until paper smokes.
Solid wax melting, flowing up the wick, and evaporating.
The burning of wax vapour itself, producing the flame — happening at the same time.
The original can be recovered — melted ice can be refrozen, vapour condensed back.
The original form can't be recovered — chopped vegetables, or popcorn made from corn.
Milk turning to curd, fruit ripening, cooking food.
Rusting of iron, food decay — though the same change can be useful in a compost pit.
Temperature swings, root growth, freezing water, and chemical reactions slowly break rocks into soil.
Wind and flowing water carry away broken rock and soil, reshaping the land over time.
Shape, size, or state changes; no new substance.
One or more new substances form.
Reacting with oxygen, releasing heat and/or light.
The lowest temperature a substance catches fire at.
The original substance can be recovered.
The original form cannot be recovered.
Rocks broken down by physical and chemical action.
Broken-down material carried away by wind or water.