12-3 Liquids and Solids Liquids The kinetic theory also can be used to explain liquid and solid behavior. Liquids have attractive forces between molecules and as the temperature (KE) decreases, the forces win and cause the molecules to move around each other freely, but stick together as a liquid. Liquids are considered incompressible. Liquids take the shape of their container, but unlike gases do not expand to fill their container.

Viscosity Viscosity is the resistance, of a liquid to flow. Syrup flows slower than water…syrup has a high viscosity. In liquids, the stronger the intermolecular forces, the higher the viscosity. The larger a molecule, generally the higher the viscosity…long chain molecules have high viscosity. Viscosity decreases with an increase in temperature.

Surface Tension, Cohesion, and Adhesion The energy required to increase the surface area of a liquid, a certain amount is called surface tension. Generally, the stronger the intermolecular attractions, the stronger the surface tension. Chemicals that break or decrease surface tension are called surfactants. Cohesion is the sticking together of like molecules. Adhesion is the sticking of one molecule to another surface or substance. Adhesion causes capillary action, or sticking/climbing of a liquid in a narrow container.

Solids Solids are generally more closely packed and dense than liquids or gases. Many solids are crystalline…they have a lattice of atoms that form a strongly bound 3-D shape. A unit-cell is the smallest repeating pattern of a crystal lattice. Some solids lack crystal structure and are amorphous. Covalent compounds are not crystalline, except for network solids, some large molecules like sugars, and for some, as they ‘freeze’ they become crystalline in nature.

12-4 Phase Changes

Water Phase Changes

State Changes fusion, melting: solid to liquid phase change boiling, vaporization: liquid to gas phase change **evaporation: liquid to gas phase change of the particles on uncontained liquids only solidification, freezing: liquid to solid phase change condensation: gas to liquid phase change sublimation: Solid to gas phase change deposition: gas to solid

Melting Point, Freezing Point, Boiling Point When ‘point’ is added to a state-change, this refers to the temperature at which the state-change occurs.

Vapor Pressure Vapor pressure is the pressure, in a sealed container or space, caused by the vaporization of a contained liquid. Vapor pressure is measured with a manometer.

Exothermic/Endothermic Nature Freezing, condensation, and deposition release energy to occur….Exothermic. Boiling, melting, sublimation absorb energy to occur…they are endothermic.

Phase Diagrams and Triple Point

Phase Diagram A phase diagram is a graphic of pressure-v- temperature that shows where solid, liquid, and gas states exist. Triple-point is the location where all three states of matter exist at one time and place.