Chapter 12 Liquids and Solids

Sect. 12-1: Liquids Properties of liquids Definite volume Takes shape of its container Properties can be explained by the kinetic molecular theory (KMT) just like gases were explained Fluid – has the ability to flow

Properties of liquids (con’t) Relatively high density Relative incompressibility Ability to diffuse Surface tension – force that tends to pull adjacent parts of a liquid’s surface together, thereby decreasing surface area to the smallest possible size

More properties of liquids… Capillary action – the attraction of the surface of a liquid to the surface of a solid Vaporization – liquid changes to a gas Evaporation – vaporization occurring at the surface of a non-boiling liquid Freezing – liquid changing to a solid

Sect. 12-2: Solids Properties of solids Definite volume Definite shape Properties can be explained by the kinetic molecular theory (KMT) just like gases and liquids were explained

Two types of solids Crystalline solids – made up of crystals Crystals – particles are arranged in an orderly, geometric fashion Amorphous solids – particles are arranged randomly

More properties of solids… Definite melting point – temperature at which a crystalline solid turns into a liquid Supercooled liquids – substances that retain certain liquid properties even at temperatures at which they appear to be solid (amorphous solids) High density Incompressibility Very low rate of diffusion

Crystalline solids Crystal structure – total 3D arrangement of particles of a crystal Unit cell – smallest part of a crystal structure that shows the 3D pattern of the entire structure

Binding forces in crystals Ionic crystals Covalent network crystals Metallic crystals Covalent molecular crystals

Sect.12-3: Changes of State Equilibrium – a dynamic condition in which two opposing changes occur at equal rates in a closed system Phase – any part of a system that has uniform composition and properties

Equilibrium and changes of state If you start out with a closed container of liquid, eventually some of it will evaporate. Over time, some of the gas will condense. If left for a long enough period of time, equilibrium will be reached for amount of substance condensing vs. evaporating. Represented by the following equation: liquid + heat energy  vapor

System will stay at equilibrium until some outside force acts upon it. Le Châtelier’s Principle – when a system at equilibrium is disturbed by an application of stress, it attains a new equilibrium position that minimizes the stress Stress is typically a change in concentration, pressure, or temperature.

Equilibrium and temperature What will happen to earlier discussed liquid/vapor system if temperature is increased? Which reaction will be favored? What if temp is decreased? Which reaction is favored?

Equilibrium and concentration What would happen to system if volume of container was suddenly increased? Amount of vapor would now be in lower concentration and thus less condensation would be occurring and more evaporation occurring until system reaches equilibrium again. At the new equilibrium, there fewer liquid molecules, but the same concentration of the gas due to larger container size. (equilibrium has shifted right)

Equilibrium and Vapor Pressure of Liquid Equilibrium vapor pressure – pressure exerted by a vapor in equilibrium over a liquid at a given temperature (increases as temp increases) Explained by KMT Pg. 376 for illustration

Volatile vs. nonvolatile liquids Volatile liquid – liquids which evaporate very easily due to weak forces of attraction between particles Have a relatively high equilibrium vapor pressure Nonvolatile liquids have stronger forces of attraction and lower equilibrium vapor pressures

Boiling Boiling – conversion of a liquid to a gas at the surface and throughout the liquid Boiling point – temperature at which the equilibrium vapor pressure is equal to the atmospheric pressure Pressure affects the boiling point Normal boiling point is at 1 atm pressure

During a phase change, such as vaporization, the temperature remains constant because any heat being added is going to changing the particles from liquid to gas Molar heat of vaporization – amount of heat required to vaporize one mole of liquid at its boiling point The higher it is, the stronger the bonds are that hold that liquid together

Freezing and Melting Freezing point – temperature at which the solid and liquid are in equilibrium at 1 atm Molar heat of fusion – amount of heat required to melt one mole of a solid at its melting point

Sublimation – change of state from a solid directly to a gas Deposition – change of state from a gas directly to a solid Both occur at low pressures and temperatures where a liquid cannot exist

Phase Diagrams Phase diagram – a graph of pressure vs. temperature that shows the conditions under which the phases of a substance exist

Triple point – indicates the temperature and pressure at which the solid, liquid, and vapor can coexist at equilibrium Critical point – indicates critical temp. and pressure Critical temperature (tc)– temp above which a substance cannot exist as a liquid Critical pressure (Pc) – lowest pressure at which the substance can exist as a liquid at the critical temperature

Sect. 12-4: Water Water molecules have a bent structure Solid or liquid water molecules are linked by hydrogen bonding Ice is made up of water arranged in hexagon shapes; this allows for low density

Physical Properties of Water Liquid water is odorless, tasteless, & transparent Relatively high molar heat of fusion (6.009 kJ/mol) Relatively high boiling point and molar heat of vaporization (40.79 kJ/mol) compared to other substances that have similar molar masses (because of hydrogen bonding)