States of Matter—Gases, Liquids and Solids

The Kinetic Molecular TheoryThe theory of moving molecules

-Use to explain the properties of solids, liquids, and gases in terms of the energy of particles and the forces that act between them

The Kinetic Molecular TheoryMajor points: Supports the concept of an ideal gas…

An ideal gas is one that perfectly fits all the assumptions of the kinetic-molecular theory.

Do not actually exist—in theory this is how they would behave:

The Kinetic Molecular Theory

1. Gases consist of large numbers of tiny particles that are far apart relative to their size.

2. Collisions between gas particles and between particles and container walls are elastic collisions. Elastic collisions one in which there is no net loss of total kinetic energy.

3. Gas particles are in continuous, rapid, random motion. They possess kinetic energy, the energy of motion.

4. There are no attractive forces between molecules (under normal conditions of temperature and

pressure)5. All gases at the same temperature have the same

average kinetic energy of particles.

Ke = ½ mv2

Ke = the kinetic energy m = mass v = the velocity

The Kinetic Molecular Theory

Applies only to ideal gases

Most gases behave like an ideal gas under normal conditions

Gases with little attraction between molecules…He/H2/N2

Real gases

Deviate from ideal behavior

Due to intermolecular interaction (H2O, NH3)

High pressureLow temperature

The Kinetic Theory and Changes of State

Gases—Attractions are insignificant

Liquids—Attractions are more important leading to a more ordered state

Solids –Attractions are most important with an ordered state

Kinetic Molecular Theory and Changes of State

Solids, liquids and gases can undergo various changes in processes that are either endothermic or exothermic

Kinetic Molecular Theory and Changes of State

Kinetic Molecular Theory and Changes of State

The amount of heat energy required to melt one mole of a solid at the solid’s melting point is the solid’s molar enthalpy of fusion.

HfEnergy absorbed

represents potential energy

For water it is 6.009kJ/mol

Xj/g =6.009kJ/M x 1M/18g x 1000J/1kJ

= 333.8 j/g

Kinetic Molecular Theory and Changes of State

The amount of heat energy required to vaporize one mole of a liquid at the liquid’s boiling point is the liquid’s molar enthalpy of vaporization.

HvEnergy absorbed

represents potential energy

For water it is 40.79kJ/mol

Xj/g =40.79J/M x 1M/18g x 1000J/1kJ

= 2266 j/g

Solids and the Kinetic Molecular theory (10.4)Properties: Dominated by the fact that

Closely packed particlesRelatively fixed positionsHighest intermolecular or interatomic attractions

Properties areDefinite shape and volumeDefinite melting pointHigh density and incompressibilityLow rate of diffusion

Solid structureSolids may be crystalline Solids may be

amorphousCrystals in which particles

are arranged in a regular repeating pattern

Particles are randomly arranged

Solid structureCrystalsTotal 3-D arrangement

of particles is the crystal structureCUBICBODY CENTERED

CUBICTETRGONALHEXAGONALTRIGONALMONO

4-Classes of Crystalline Solids

Ionic --Ions Hard and Britle

Covalent NetworkNetwork of

moleculesQuartz (SiO)Diamond

Metallic CrystalsFree moving e-

Covalent Molecular Crystals

Weak….Water, dry ice

Amorphous solidsWithout shape No regular patternGlasses Plastics

Kinetic Molecular Theory and Changes of State (Water- 10.5)

Compared to other substances water has a high specific heat.

Water has very strong intermolecular bonding

Hydrogen bonds between highly polar molecules

Changes of State are Shown in Phase Diagrams

Changes of phase are depicted in phase diagrams

Show the relationship between state of matter, temperature and pressure

Changes of State Shown in Phase Diagrams

Phase diagrams define:

Triple point=the T/P conditions at which all three phases coexist

Critical point = Critical temp and press

Critical temp = temp above which the substance cannot exist as a liquid

Critical press= lowest pressure at which the substance can exist as a liquid at the critical temperature

Phase Diagram of WaterInteresting pointsAD—Ice and vapor in

equilibriumAC– Liquid and vapor

in equilibriumAB—Ice and liquid in

equilibrium. Note an increase in pressure lowers melting point

nbp=normal boiling ptmp =melting pointCritical temp =373.99

Phase Diagram of Carbon Dioxide

Note the following:

Very different temp and pressure compared to water’s diagram

Liquid is only possible at high pressure

At normal room conditions CO2 only exists as a gas

Phase Change vs Temperature change in a single phaseMelting/Fusion

…Molar heat of fusion6.009 kJ/mol

VaporizingMolar hear of

vaporization40.79kJ/mol

Raising the temperature of a homogeneous materialSpecific heat

Phase ChangeHow much energy is absorbed when 47g of

ice melts? (at STP)

Energy =47g x 1 mol x 6.009kJ

18g 1 mol

= 15.7 kJ

Phase ChangeHow much energy is absorbed when 47g of

water vaporizes? (at STP)

Energy =47g x 1 mol x 40.79kJ

18g 1 mol

= 106 kJ (vs 15.7 kJ—gases have a higher energy content)

Phase ChangeWhat mass of steam is required to release

4.97 x 105kJ of energy when it condenses?

grams =4.97 x 105kJ x 1mol x 18g

40.79kJ 1 mol

= 2.19 x 105 g

Temperature change in a single phaseSpecific heat of

water , Cp

Definition… the quantity of heat (q) required to raise 1 gram of water 1oC at a constant pressure.

Value will vary for each substance

Temperature change in a single phaseQuantity of energy

transferred as heat while a temperature change occurs depends on

The nature of the substance

The mass of the material

The size of the temperature change.

Water has a high specific heat

Metals have low specific heat

Units = J/(g x oC)

Temperature change in a single phaseSpecific heat of water (l) = 4.18 J/goCSpecific heat of water (s) = 2.06Specific heat of water (g) = 1.87Specific heat of ethanol (g) = 1.42Specific heat of ethanol (l) = 2.44Specific heat of mercury (l) = 0.140Specific heat of copper (s) = 0.385Specific heat of lead (s) = 0.129Specific heat of aluminum (s) = 0.897