Glossary
states of matter
The states of matter are solid, liquid and gas: a solid holds its own shape and volume, a liquid holds its volume but takes the shape of its container, and a gas holds neither.
The states of matter are the three forms a substance can take, and they differ in how tightly their particles are held. In a solid the particles are packed in a fixed arrangement, so a solid keeps both its shape and its volume. In a liquid the particles are still close but free to slide, so a liquid keeps its volume and takes the shape of whatever holds it. In a gas the particles are far apart and moving fast, so a gas fills its container and can be compressed.
The names of the changes between them are worth having: melting (solid to liquid), freezing (liquid to solid), evaporation and boiling (liquid to gas), condensation (gas to liquid), and sublimation (solid straight to gas, as dry ice does).
Every one of those changes is a physical change, because the substance is the same afterwards — steam is still water. Melting, boiling and evaporating take heat in, while freezing and condensing give heat back out, and a question that asks which process warms its surroundings is asking about condensation or freezing.
Taught in
Related terms
- water cycle — The water cycle is the endless movement of water between the ocean, the air and the land — evaporation, condensation, precipitation, and runoff or infiltration back to the sea.
- physical change — A physical change alters a substance's size, shape or state — melting, freezing, dissolving, tearing — without making a new substance. The material is the same before and after.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)