States of matter, physical vs. chemical properties, and the changes that move a substance between them — the one distinction that decides almost every question here is whether a new substance formed. Every question comes with a written explanation of exactly what changed.
Dissolving sugar in water, melting ice, or crushing a rock all look significant but don't create a new substance — the test is whether a new substance formed, not how dramatic the change looks.
Sublimation is a solid turning directly into a gas, skipping the liquid state entirely (like dry ice); evaporation is specifically a liquid turning into a gas — the two start from different states.
Flammability is a chemical property because you can only confirm it by actually burning the substance — you can describe it, but proving it requires watching the reaction happen.
Straight from the bank — one per difficulty tier. Reveal the answer to see the explanation you'd get in a real session.
Which of the following is an example of a chemical change?
Dry ice (solid carbon dioxide) is left out at room temperature and turns directly into carbon dioxide gas, without ever becoming a liquid. What is this phase change called?
A student burns 10 grams of wood in a sealed, airtight container along with enough oxygen for complete combustion, then weighs everything remaining inside the container — ash, gases, and unused oxygen. Based on the law of conservation of mass, what should the total mass be, and why?
Matter and properties questions reward one habit above all: asking whether a new substance actually formed before calling something a chemical change.
For every change described, decide whether a new substance was created before labeling it physical or chemical. Untimed practice is where that single question becomes automatic.
Move to timed sessions once physical-vs-chemical classification is instant.
Pair matter and properties with chemical reactions in a mock — both hinge on the same new-substance test.
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