States of Matter introduces the particle model of matter and explains properties of solids, liquids, and gases. It covers changes of state, diffusion, and gas behaviour — the foundation of all chemistry.
Solids: particles closely packed in fixed positions, vibrate about fixed points, strong forces between particles. Liquids: particles close but can move past each other, weaker forces than solids. Gases: particles far apart, move randomly at high speed, negligible forces. The model explains properties: solids have fixed shape and volume; liquids have fixed volume but take shape of container; gases fill any container and are compressible.
Melting (solid → liquid), boiling/evaporating (liquid → gas), condensing (gas → liquid), freezing (liquid → solid), sublimation (solid → gas directly). During changes of state: temperature remains constant (energy used to break/form bonds, not increase KE). Heating curve: flat sections show melting/boiling points. Evaporation occurs at any temperature from the surface; boiling occurs throughout the liquid at a specific temperature.
Diffusion: net movement of particles from high concentration to low concentration. Evidence: bromine gas spreading in air, potassium manganate(VII) in water. Rate of diffusion: lighter molecules faster (Graham\'s law). Gas pressure caused by particle collisions with container walls. Boyle\'s law (Supplement): pV = constant at constant temperature. Pressure increases with temperature (more collisions).
Evaporation occurs at any temperature from the surface of a liquid — faster-moving particles escape. Boiling occurs at a fixed temperature (boiling point) throughout the liquid, with bubbles of vapour forming inside. Evaporation is slower and causes cooling (average KE of remaining particles decreases). Boiling requires continuous energy input. Both are liquid → gas transitions, but boiling only happens at the boiling point.
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