Chapter 10 States of Matter

• The Nature of Gases• The Nature of Liquids• The Nature of Solids• Changes of State

Ch 10.1 The Nature of Gases

• Kinetic Theory• Gas Pressure• Kinetic Energy and

Kelvin Temperature

Kinetic Theory

• Name the three states of matter:– Solid

– Liquid

– Gas

• How do you change phase?– Change Temperature

Kinetic Theory

• Kinetic Energy – The energy an object has due to motion

• Kinetic Theory – Particles in all forms of matter are in constant motion

Assumptions of the Kinetic Theory as applies to Gases

1) A gas is composed of molecules or atoms that have insignificant volume and are spread very far apart. In between is empty space. No attractive or repulsive forces exist.

2) The particles in a gas move rapidly in constant random motion.

a) Travel in straight paths.

b) Change direction only when they collide.

Assumptions of the Kinetic Theory as applies to Gases

3) All collisions are perfectly elastic. Kinetic energy is transferred. It is never lost.

Gas Pressure

• Gas Pressure – force exerted by a gas per unit of surface area.

• Atmospheric Pressure – results from collisions of air molecules with objects

• Barometers – measure atmospheric pressure

Gas Pressure Units

• SI Units – pascal (Pa) sea level = 101.3 kPa• Older Units – millimeters Mercury (mm Hg)

- Atmospheres (atm)

101.3 kPa = 760 mm Hg = 1 atm

Kinetic Energy and Kelvin Temperature

• An increase in KE causes an increase in temperature. Particles speed up.

• A decrease in KE causes a decrease in temperature. Particles slow down.– At –273.15ºC ( 0 K) all particles stop moving =

absolute zero.

Kinetic Energy and Kelvin Temperature

• Direct relationship– Particles in helium at 200 K have twice as much KE as

particles at 100 K.

Ch 10.2 The Nature of Liquids

• A Model of Liquids• Evaporation• Boiling Point

A Model of Liquids

• Particles in a liquid are moving.

• They slide past each other.

• They can flow• But, they are attracted

to each other – intermolecular forces

A Model of Liquids

• The particles in a liquid vibrate and spin while they move around.

• All three of these motions contribute to the average Kinetic Energy.

• In order to become a gas, the liquid particles must have enough KE to overcome the intermolecular forces.

A Model of Liquids

• Intermolecular forces – cause liquid particles to be closer together. – More dense than gases

• Increasing pressure has no effect on the volume of a liquid.

Evaporation

• Vaporization - conversion of a liquid to a gas or vapor

• Evaporation – the process of vaporization occurring at the surface of a liquid when it is not boiling.

Evaporation

• Why do liquids evaporate faster when heated?• The added heat increases the KE of the liquids

particles which allows the particles to overcome the intermolecular forces.

• Evaporation is a cooling process – WHY?• The particles with the most heat escape first

leaving those particles with less heat behind. The liquids temperature will decrease.

Vapor Pressure

• A force due to the gas above a liquid.

Boiling Point

• The point where vapor pressure of the liquid is just equal to the external pressure.

• Boiling Points will change if the external pressure changes.

• Normal Boiling Point – the boiling point of a liquid at 101.3 kPa

Table H - Reference Table

• Normal Boiling Point of Water- – 100ºC

• Boiling Point of water at 200 kPa-– 118 ºC

• Boiling Point of water at 50 kPa-– 82 ºC

• Describe the effect of pressure on waters boiling point.

Table H - Reference TableNormal bp

Bp at 50 kPa

Bp at 150 kPa

Bp at 200 kPa

Propanone

Ethanol

Water

Ethanoic Acid

Table H - Reference TableVP at 25 ºC

VP at 50ºC

VP at 75 ºC

VP at 100 ºC

Propanone

Ethanol

Water

Ethanoic Acid

High Altitude Cooking

• Most high altitude cooking and baking instructions do not recommend compensations until you reach about 6000 ft above sea level.

• Water boils at a lower temperature here - this is due to reduced air pressure.

• Takes longer to cook food.

High Altitude Cooking

Chapter 10.3

• A Model for Solids• Crystal Structure and Unit Cells

A Model for Solids

• Describe the movement of particles in a solid:– Vibrate around fixed points

 

• Describe the structure of particles in a solid:– Packed against one another in a highly organized pattern

 

• The density of liquids is ___high__.

• Are solids compressible?– NO 

A Model for Solids

• Can solids flow?– NO 

• What does flow mean?– To move with a continual shifting of the component

particles

A Model for Solids

• What 3 things happen when you heat a solid?• 1) Particles vibrate more • 2) Organization of particles breaks down • 3) Melts

A Model for Solids

• Define melting point: – Temperature at which a solid becomes a liquid

• Describe what the disruptive vibrations do at the melting point: – Overcome interactions that hold the particles in a fixed postion

• Fill in the diagram:  melting

Solid Liquid

freezing

A Model for Solids

• Describe the melting points of:– Ionic Solids: High

–   Molecular Solids: Low

 • What is an ionic solid?

– Metal and nonmetal 

• What is a molecular solid?– Two nonmetals

Crystal Structure and Unit Cells

• Define crystal: – Atoms, ions or molecules arranged in an orderly,

repeating, three dimensional pattern called the crystal lattice

• What determines the melting points of crystals? – Type of bonding between atoms

• What determines the shape of a crystal? – Arrangement of particles within it

Crystal Structure and Unit Cells

• List the 7 types of crystal systems:– Cubic

– Tetragonal

– Orthorhombic

– Monoclinic

– Triclinic

– Hexagonal

– Rhombohedal

Crystal Structure and Unit Cells

• Define unit cell: – Smallest group of particles within a crystal that retains the

geometric shape

• List the three forms of pure carbon: – Diamond

– Graphite

– buckyball

• What is an allotrope? – Two or more different forms of the same element

Crystal Structure and Unit Cells

• What is an amorphous solid? – Solid that lacks an ordered internal structure

• List examples of amorphous solids: – Rubber, plastic, asphalt, glass

• Describe glasses and associated properties: – Super cooled liquids

– Between a crystalline solid and a liquid

– Doesn’t have a true melting point.

Answer these questions in your notes

• How are the solid, liquid and gas states of water related on Earth?

• What does freeze dried mean?

• Why are freeze dried foods important?

Ch 10.4 Changes of State

• Phase Diagrams• Sublimation

Phase Diagrams

• Gives the conditions of temperature and pressure at which a substance exist as a solid, liquid or gas

• Triple Point – The set of conditions when all three forms can exist

                                                                                   

Normal Melting Point

Normal Boiling Point

Triple Point

Sublimation

• Can you dry your wash on a clothesline (outside) during winter?– Yes, your clothes will freeze solid, but then the ice will

sublime into a vapor.

• Sublimation – Change of a solid directly to a gas

Used to make freeze dried foods.

Dry Ice (-78ºC)

Solid Air Fresheners

Mothballs “Grandma’s House”

Phase Change Diagram