Phases of Matter

Solids matter is arranged in a regular, rigid pattern definite shape and volume crystalline structure

Liquids particles not held as tightly together able to move past one another (flow) definite volume, no definite shape

Gases Minimal attractive forces holding particles together No definite shape or volume (takes the shape and volume of a container)

Phase Changes all phase changes are accompanied with either a loss or gain of energy an element, compound, or mixture can exist as a solid, liquid, or gas (s, l, g)

Endothermic Changes Phase changes that require the gain of heat Examples 1. melting/fusion- solid substance becomes liquid 2. evaporation/boiling/vaporization- liquid substance becomes gas 3. sublimation- solid substance changes directly to a gas

Exothermic Reactions all of these phase changes require the loss or release of energy Examples 1. freezing/solidification – liquid substance becomes solid 2. condensation – gaseous substance becomes liquid 3. deposition – gaseous substance turns directly into a solid

Phases In Detail Solids

True solids have a crystalline structure 1. Crystals are arranged in repeated geometric patterns 2. Example: ice (strong intermolecular attraction)

Pseudosolids lack crystalline structure 1. Examples: glass, some plastics 2. These are supercooled liquids

Sublimation When a solid changes directly into a gas by the addition of heat Substances that sublime have high vapor pressure (lots of gas hovering over the solid) Low intermolecular forces of attraction (particles break apart easily) Examples: 1. Dry ice (frozen carbon dioxide) CO 2 (s) 2. Solid iodine I 2 (s) 3. mothballs