HESI A2 · Chemistry · 6 min read
Matter: States, Properties, Changes and Mixtures
- Differentiate between the fundamental states of matter and identify their structural characteristics and phase transitions.
- Distinguish between physical and chemical properties and classify them as intensive or extensive.
- Categorize types of matter into elements, compounds, and mixtures, and select appropriate physical methods for separating mixtures.
The Nature and Fundamental States of Matter
Matter is formally defined as anything that has mass and takes up space. In our physical environment, matter is encountered in several distinct forms known as states. The four common fundamental states of matter are solid, liquid, gas, and plasma. The distinct behavior of each state arises from the arrangement and mobility of its underlying particles.
A solid has a definite shape and a definite volume. The particles in a solid are tightly packed together and vibrate in fixed positions rather than moving freely, which allows the solid to maintain its distinct structure regardless of its surroundings. In contrast, a liquid has a definite volume but adapts to the shape of its container. The particles within a liquid are closely packed, but they are able to flow and slide past one another.
A gas has neither a definite shape nor a definite volume and expands to fill its container completely. Gas particles are located far apart from one another and move rapidly in continuous, random motion. The fourth state, plasma, is an ionized gas that contains free electrons and positive ions.
Because of these fundamental structural differences, states of matter respond differently to pressure. Gases are highly compressible because their particles are separated by vast amounts of space. Conversely, solids and liquids are relatively incompressible because their particles are already closely packed together.
Common mistakes
- Assuming that signs such as a color change, gas production, or temperature change definitively prove a chemical change occurred, when none alone provides absolute proof.
- Believing that dissolving table salt in water is a chemical change; it is a physical change because the chemical identity of the salt is not altered.
- Classifying density as an extensive property because it involves mass and volume; density is an intensive property because the ratio of mass to volume does not depend on the amount of matter.
- Confusing colloids with solutions; colloids are heterogeneous mixtures with intermediate particle sizes that do not settle out but do scatter light via the Tyndall effect.
Key points
- Matter is defined as anything that has mass and takes up space, existing as solids, liquids, gases, and plasma.
- Gases are highly compressible and lack definite shape and volume, whereas solids and liquids have definite volume and are relatively incompressible.
- Physical properties can be intensive (independent of sample size, such as density and boiling point) or extensive (dependent on sample size, such as mass and volume).
- Chemical properties describe a substance's potential to undergo chemical change (such as flammability and reactivity with water), while inertness denotes a lack of reactivity.
- Phase transitions and dissolving table salt in water are physical changes, whereas rusting of iron and combustion of fuels are chemical changes that produce new substances.
- Pure substances include elements and chemically combined compounds, while mixtures are physical combinations of substances with variable proportions that retain their individual identities.
- Mixtures can be separated physically using filtration, decantation, centrifugation, evaporation, simple and fractional distillation, and chromatography.
Practice this section
Explained HESI Chemistry questions, no account needed. HESI Chemistry practice test
The full lesson continues with 4 more sections with exam tips, audio in English and Spanish, 5 Check yourself questions and 20 flashcards.
- 1 month
$53.99$26.99 - 3 months
$158.99$79.49 - Lifetime
$323.99$161.99
One payment, no subscription.
See HESI plansAlready a member? Log in
Sample lesson: Atomic Structure and Isotopes25 practice questions on this exam
Each HESI practice test has 25 original questions with the answers explained. No account needed.
Open the HESI practice testsOriginal lesson written for HESI A2 practice · updated October 15, 2026. Exam names are trademarks of their owners; tests.global is not affiliated with them.