Transcript The Kinetic Molecular Theory

States of Matter—Gases, Liquids and Solids
The Kinetic Molecular Theory
The 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 Theory
Major 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
 Real gases
gases
 Deviate from ideal
 Most gases behave like
an ideal gas under
normal conditions
 Gases with little
attraction between
molecules…He/H2/N2
behavior
 Due to intermolecular
interaction (H2O, NH3)
 High pressure
 Low 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
 For water it is 6.009kJ/mol
energy required to melt
one mole of a solid at the  Xj/g =6.009kJ/M x 1M/18g x 1000J/1kJ
solid’s melting point is
the solid’s molar

= 333.8 j/g
enthalpy of fusion.
 DHf
 Energy absorbed
represents potential
energy
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.
 DHv
 Energy 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 particles
 Relatively fixed positions
 Highest intermolecular or interatomic attractions
 Properties are
 Definite shape and volume
 Definite melting point
 High density and incompressibility
 Low rate of diffusion
Solid structure
Solids may be crystalline
Solids may be amorphous
Crystals in which particles are
arranged in a regular
repeating pattern
Particles are randomly arranged
Solid structure
Crystals
 Total 3-D arrangement of
particles is the crystal
structure
 CUBIC
 BODY CENTERED CUBIC
 TETRGONAL
 HEXAGONAL
 TRIGONAL
 MONO
4-Classes of Crystalline Solids
Ionic
--Ions
Hard and Britle
Covalent Network
Network of molecules
Quartz (SiO)
Diamond
Metallic Crystals
Free moving eCovalent Molecular Crystals
Weak….
Water, dry ice
Amorphous solids
Without shape
No regular pattern
 Glasses
 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 Water
 Interesting points
 AD—Ice and vapor in





equilibrium
AC– Liquid and vapor in
equilibrium
AB—Ice and liquid in
equilibrium. Note
an increase in pressure
lowers melting point
nbp=normal boiling pt
mp =melting point
Critical 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 phase
 Melting/Fusion
 …Molar heat of fusion
 6.009 kJ/mol
 Vaporizing
 Molar hear of vaporization
 40.79kJ/mol
 Raising the temperature of a
homogeneous material
 Specific heat
Phase Change
 How much energy is absorbed when 47g of ice melts?
(at STP)
 Energy =47g x 1 mol x 6.009kJ
18g
= 15.7 kJ
1 mol
Phase Change
 How much energy is absorbed when 47g of water
vaporizes? (at STP)
 Energy =47g x 1 mol x 40.79kJ
18g
= 106 kJ
1 mol
(vs 15.7 kJ—gases have a
higher energy content)
Phase Change
 What mass of steam is required to release 4.97 x 105kJ
of energy when it condenses?
 grams =4.97 x 105kJ x 1mol
40.79kJ
= 2.19 x 105 g
x 18g
1 mol
Temperature change in a single phase
 Specific 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 phase
 Quantity 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 phase
 Specific heat of water (l)
= 4.18 J/goC
 Specific heat of water (s)
= 2.06
 Specific heat of water (g)
= 1.87
 Specific heat of ethanol (g) = 1.42
 Specific heat of ethanol (l)
= 2.44
 Specific heat of mercury (l) = 0.140
 Specific heat of copper (s)
= 0.385
 Specific heat of lead (s)
= 0.129
 Specific heat of aluminum (s) = 0.897