Liquids and Solids Chapter 13

The States of Matter

Liquids - Properties of Liquids: Definite volume (density g/mL) Fluidity Non-compressibility Diffusion (miscible) Evaporation

Kinetic Molecular Theory description: Lots of evidence for molecular motion (Brownian motion and diffusion) Density is much greater than in gases --- molecules are closer IM forces are more important than in gases Strength of IM forces reflected in liquid temp. range and in vapor pressure nonpolar covalent molecules – weakest IM and highest VP polar covalent molecules - medium range hydrogen bonding - unusually high IM and low VP metallic liquids - very high IM and very low VP strong enough to keep fluid but weak enough to allow random particle motion IM forces are strong enough to keep fluidity but weak enough to allow random particle motion

Surface Tension Attractive force which pulls the surface molecules of a liquid together Cohesion Causes droplets to be spherical Greatest ratio of volume to surface area. Insects can walk on water. Water has very high surface tension due to the high IM forces (H-bonding)

Surface tension

Capillary Action Attraction of the surface of a liquid to the surface of its container. Adhesion Causes the meniscus in glassware. Water stays in the bottom of a straw. Paper towels “wick” away the water. Mercury has an inverted meniscus.

Meniscus

Diffusion One liquid spreads (dissolve) throughout another if they have similar molecules (polar or nonpolar) Slower than in gases Temperature matters Food coloring demo in hot vs. cold water

Evaporation Surface event only. Molecules on the surface with highest KE can escape the liquid phase. Results in lower avg. KE for the liquid remaining (cooler temp) Perspiration is a cooling event.

Evaporation

High temp. Low temp. % of Molecules Kinetic Energy

Rate of Evaporation Increase rate by: 1. heat sample 2. increase surface area 3. blow air over the surface Race on board alcohol vs. water vs acetone

Crystalline or Amorphous??? Solids Crystalline or Amorphous???

SOLIDS - General Properties: Definite shape – non-fluid Definite volume – all surfaces are free – density (g/cm3) Non-compressible Very slow diffusion (if any)

Crystalline Solids Particles are arranged in a repeating pattern Crystal lattice Specific melting point Smallest repeating unit is called the “unit cell” Several basic types which give facets to gemstones

Unit Cells in the Cubic Crystal System

Lattice energy Energy req. to separate the crystal lattice. This determines the strength and hardness of the crystal and the MP and BP. Four crystal categories Covalent network -highest MP Ionic -high MP Metallic -med. to high MP Covalent molecular -lowest MP

Amorphous solids random arrangement of particles MP and BP are not sharply defined Glass, plastics, some semiconductors

KMT description of solids: molecules are fixed in position vibrational and/or rotational motion only KE is related to temp. - as temp increases so does KE.

Phase Changes Change in arrangement of the particles Requires PE changes Temp. stays constant during a phase change. (MP or BP) Plateau on temp./time graphs

Solid Gas Liquid Sublimation Melting Vaporization Freezing Endothermic processes Sublimation Vaporization Melting Solid Liquid Gas Deposition Freezing Condensation Exothermic processes

Dynamic Equilibrium In a closed container the vapor will develop a DYNAMIC EQUILIBRIUM.

Dynamic Equilibrium- A physical state where two opposing processes occur at equal rates in the same system. Ex. In a sealed bottle half full of water……… liquid + energy ↔ vapor vapor ↔ liquid + energy ****must have a closed system for an equilibrium to occur.

Vapor Pressure (VP) Once equilibrium occurs the vapor exerts a constant pressure on the container VP is dependent on the temperature of the system and the type of liquid, but not the volume of the container.

Boiling Not the same as evaporation Occurs throughout the liquid Rapid change of state. VP is equal to pressure above the liquid so bubbles form and are not collapsed on the way to the surface. Standard BP occurs at 1 atm.

KE and PE in phase changes During a phase change, temperature remains constant →KE constant, PE changes Energy is used to change arrangements of particles not speed. During heating/cooling, temperature changes → KE changes, PE is constant

Heating Curve for Water and Ice Ice Water and Steam Steam -20 20 40 60 80 100 120 220 760 800 Heating Curve for Water KE Change PE change KE Change Temp C PE change KE Change Time

Calculating Energy (J or kJ) Three equations Heat = heat of fusion x mass Heat = heat of vaporization x mass Heat = specific heat x mass x DT

Energy and Phase Change Heat of fusion: energy required to change one gram of a substance from solid to liquid. Heat of crystallization: energy released when one gram of a substance changes from liquid to solid. For water: 80 cal/g or 334 J/g

Energy and Phase Change Heat of vaporization: energy required to change one gram of a substance from liquid to gas. Heat of condensation: energy released when one gram of a substance changes from gas to liquid. For water 540 cal/g or 2260 J/g

Phase diagrams