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Phases and Phase Changes. Solid. Has a definite shape and volume. Particles that make up a solid are packed together in relatively fixed positions and are held together by strong attractive forces between them. . Liquid.
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Solid • Has a definite shape and volume. Particles that make up a solid are packed together in relatively fixed positions and are held together by strong attractive forces between them.
Liquid • Has a definite volume but an indefinite shape (it assumes the shape of its container). Particles are close together but can move past one another. They move more rapidly than in a solid. This allows them to temporarily overcome the attractive forces and allows liquid to flow
Gas • Has neither a definite shape or volume. It will fill its container. Particles move very rapidly and are at great distances from each other. Attractive forces become very weak.
Physical Properties • Characteristics that can be observed or measured without changing the identity of the substance. They describe the substance. • Ex: Boiling point, Melting point
Physical Change • It does not involve a change in the identity of the substance. • Ex: Grinding, cutting, melting, boiling
Chemical Properties • Relates to a substance’s ability to undergo changes that transform it into different substances. • Easiest to see when substances react to form new substances. • Ex: Iron’s ability to rust, silver can tarnish when combined with sulfur
Chemical Change • Also known as a chemical reaction • A change in which one or more substances are converted into different substances.
Drawing of Physical Change Solid CO2 -> gaseous CO2
Drawing of Chemical Change FeO2 -> Fe + O2
Density • Density depends on how tightly the atoms/molecules are packed together
Gas – low density • The molecules are far apart; therefore, lots of volume
Liquid – higher density • Molecules are closer together, so density is higher
Solutions – higher density • Water molecules have other molecules “fitting” into spaces, increasing the mass for the same volume • This is why sugar and salt water are more dense than pure water
Phase Changes • Melting – changing from a solid to a liquid • Freezing – changing from a liquid to a solid • Evaporating – changing from a liquid to a gas • Condensing – changing from a gas to a liquid • Sublimation – changing from a solid to a gas • Deposition – changing from a gas to solid