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 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