Transcript KINETIC THEORY Unit 7 Chemistry Langley *Corresponds to Chapter 13 (pgs. 384-409) in Prentice Hall Chemistry textbook.

KINETIC THEORY
Unit 7
Chemistry
Langley
*Corresponds to Chapter 13 (pgs. 384-409) in Prentice Hall Chemistry
textbook
KINETIC THEORY
 Kinetic Theory states that the tiny
particles in all forms of matter are in
constant motion.
 Kinetic refers to motion
 Helps you understand the behavior of solid,
liquid, and gas atoms/molecules as well as
the physical properties
 Provides a model behavior based off three
principals
KINETIC THEORY

3 Principles of Kinetic Theory
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All matter is made of tiny particles (atoms)
These particles are in constant motion
When particles collide with each other or
the container, the collisions are perfectly
elastic (no energy is lost)
STATES OF MATTER
 5 States of Matter
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Solid
Liquid
Gas
Plasma
Bose-Einstein
Condensates
http://www.plasmas.org/E-4phases2.jpg
SOLIDS
 Particles are tightly packed and close together
 Particles do move but not very much
 Definite shape and definite volume (because
particles are packed closely and do not move)
 Most solids are crystals
 Crystals are made of unit cells (repeating
patterns)
 The shape of a crystal reflects the arrangement of
the particles within the solid
SOLIDS
 Unit cells put together make a crystal
lattice (skeleton for the crystal)
 Crystals are classified into seven crystal
systems: cubic, tetragonal,
orthorhombic, monoclinic, triclinic,
hexagonal, rhombohedral
 Unit cell  crystal lattice  solid
SOLIDS
 Amorphous Solid:
 A solid with no defined shape (not a crystal)
 A solid that lacks an ordered internal structure
 Examples: Clay, PlayDoh, Rubber, Glass, Plastic,
Asphalt
 Allotropes:
 Solids that appear in more than one form
 2 or more different molecular forms of the same
element in the same physical state (have different
properties)
 Example: Carbon
 Powder = Graphite
 Pencil “lead” = graphite
 Hard solid = diamond
SOLIDS
www.ohsu.edu/research/sbh/resultsimages/crystalvsglass.gif
SOLIDS
Allotropes of
Carbon: a)
diamond, b)
graphite, c)
lonsdaleite,
d)buckminsterfull
erene (buckyball),
e) C540, f) C70, g)
amorphous
carbon, and h)
single-walled
(buckytube)
www.wikipedia.org
LIQUIDS
 Particles are spread apart
 Particles move slowly through a container
 No definite shape but do have a definite
volume
 Flow from one container to another
 Viscosity – resistance of a liquid to flowing
 Honey – high viscosity
 Water – low viscosity
chemed.chem.purdue.edu/.../graphics
GASES
 Particles are very far apart
 Particles move very fast
 No definite shape and No definite volume
http://www.phy.cuhk.edu.hk/contextual/heat/tep/
trans/kinetic_theory.gif
PLASMA

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Particles are extremely far apart
Particles move extremely fast
Only exists above 3000 degrees Celsius
Basically, plasma is a hot gas
When particles collide, they break apart
into protons, neutrons, and electrons
 Occurs naturally on the sun and stars
BOSE-EINSTEIN CONDENSATE
 Particles extremely close together
 Particles barely move
 Only found at extremely cold
temperatures
 Basically Bose-Einstein is a cold solid
 Lowest energy of the 5 states/phases of
matter
GASES AND PRESSURE
 Gas pressure is the force exerted by a gas per unit
surface area of an object
 Force and number of collisions
 When there are no particles present, no collisions = no
pressure = vacuum
 Atmospheric Pressure is caused by a mixuture of gases
(i.e. the air)
 Results from gravity holding air molecules downward in/on
the Earth’s atmosphere; atmospheric pressure decreases
with altitude, increases with depth
 Barometers are devices used to measure atmospheric
pressure (contains mercury)
 Standard Pressure is average normal pressure at sea
level
 As you go ABOVE sea level, pressure is less
 As you go BELOW sea level, pressure is greater
GASES AND PRESSURE
 Standard Pressure Values
 At sea level the pressure can be recorded as:
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14.7 psi (pounds per square inch)
29.9 inHg (inches of Mercury)
760 mmHg (millimeters of Mercury)
760 torr
1 atm (atmosphere)
101.325 kPa (kilopascals)
 All of these values are EQUAL to each other:
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29.9 inHg = 101.325 kPa
760 torr = 760 mmHg
1 atm = 14.7 psi
and so on……….
 Say hello to Factor Label Method!!!!!!!!!!!!
GASES AND PRESSURE
 STP
 Standard Temperature and Pressure
 Standard Pressure values are the values listed on
the previous slides
 Standard Temperature is 0°C or 273 K
 If temperature is given to you in Farenheit, must convert
first!
 °F = (9/5)°C + 32
 °C = (5(°F-32)) / 9
Remember order of operation rules
 K = 273 + °C
 °C = K – 273
GASES AND PRESSURE
 Pressure Conversions
 Example 1: 421 torr = ? Atm
 Step 1: Write what you know
 Step 2: Draw the fence and place the given in
the top left
 Step 3: Arrange what you know from step 1 such
that the nondesired units canceling out so that
you are only left with the units you want (i.e. atm)
 Step 4: Solve
 Step 5: Report final answer taking into account
the appropriate significant figures
GASES AND PRESSURE
 Pressure Conversions
 Example 2: 32.0 psi = ? torr
TEMPERATURE
 Temperature is the measure of the average
kinetic energy of the particles.
 3 Units for Temperature:
 Celsius
 Farenheit
 Kelvin
 Has an absolute zero
 Absolute lowest possible temperature
 All particles would completely stop moving
 Temperature Conversions:
 Example 1: Convert 35°C to °F
 Example 2: Convert 300 Kelvin to °C
MEASURING PRESSURE
 Manometers:
 Measure pressure
 2 kinds: open and closed
 Open Manometers:
 Compare gas pressure to air pressure
 Example: tire gauge
 Closed Manometer:
 Directly measure the pressure (no
comparison)
 Example: barometer
KINETIC ENERGY AND
TEMPERATURE
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Energy of motion
Energy of a moving object
Matter is made of particles in motion
Particles have kinetic energy
KE = (mv2)/2
OR
KE = (ma)/2
 Kinetic Energy is measured in Joules
 1 J = 1kg•m2/s2
 The mass must be in kg
 The velocity must be in m/s OR acceleration must be in
m2/s2
KINETIC ENERGY AND
TEMPERATURE
 Calculate the KE of a car with a mass of
1500 kg and a speed of 50 m/s
KINETIC ENERGY AND
TEMPERATURE
 Calculate the KE of a car with a mass of
6780 grams and a speed of 36 km/h
KINETIC ENERGY AND
TEMPERATURE
 Temperature-measure of the average kinetic
energy of the particles
 Kelvin Scale:
 Has an absolute zero (0K)
 Absolute lowest possible temperature
 In theory, all particles would completely stop moving
 Speed of Gases:
 If two gases have the same temperature (particles
moving at the same speed) how can you tell which
gas has a greater speed?
 The only difference is mass!
 To find mass, use the periodic table
KINETIC ENERGY AND
TEMPERATURE
 Speed of Gases
 Example 1: If CH4 and NH3 are both at 284
K, which gas has a greater speed?
 Step One: Add up the mass of each gas using
the periodic table.
 Step Two: The lighter gas moves faster (think
about a race between a 100-pound man and a
700-pound man, the lighter man would move
faster)
 Example 2: Which gas has a faster speed
between Br2 and CO2 if both are at 32°F?
TERMINOLOGY for PHASE
CHANGES
 Melting-commonly used to indicate changing
from solid to liquid
 Normal melting point-The temperature at which the
vapor pressure of the solid and the vapor pressure
of the liquid are equal
 Freezing-Changing from a liquid to a solid
 Melting and freezing occur at the same
temperature
 Liquifaction-Turning a gas to a liquid
 Only happens in low temperature and high pressure
situations
TERMINOLOGY for PHASE
CHANGES
 Difference in Gas and Vapor
 Gas-state of matter that exists at normal room
temperature
 Vaport-produced by particles escaping from a state
of matter that is normally liquid or solid at room
temperature
 Boiling-used to indicate changing from a liquid
to a gas/vapor
 Normal boiling point - temperature at which the
vapor pressure of the liquid is equal to standard
atmospheric pressure, which is 101.325 kPa
 Boiling point is a function of pressure.
 At lower pressures, the boiling point is lower
TERMINOLOGY for PHASE
CHANGES
 2 types of boiling: boiling and
evaporation
 Evaporation takes place only at the surface of a
liquid or solid while boiling takes place
throughout the body of a liquid
 Particles have high kinetic energy
 Particles escape and become vapor
 Condensation-used to indicate changing
from a vapor to a liquid
TERMINOLOGY for PHASE
CHANGES
 Sublimation - when a substance changes directly from
a solid to a vapor
 The best known example is "dry ice", solid CO2
 Deposition-when a substance changes directly from a
vapor to a solid (opposite of sublimation)
 Example-formation of frost
 Dynamic equilibrium - when a vapor is in equilibrium
with its liquid as one molecule leaves the liquid to
become a vapor, another molecule leaves the vapor to
become a liquid. An equal number of molecules will be
found moving in both directions
 Equilibrium - When there is no net change in a system
TERMINOLOGY for PHASE
CHANGES
 Points to Know:
 Melting Point-Temperature when solid turns to a
liquid
 Freezing Point-Temperature when liquid turns to a
solid
 Boling Point-Temperature when a liquid turns to a
vapor
 Doesn’t boil unitl vapor pressure coming off liquid is equal
to the air pressure around it
 Since air pressure changes with height, water does not
always boil at 100°C
 Condensing Point-Tempeature when vapor turns to
liquid
ENTROPY
 A measure of the disorder of a system
 Systems tend to go from a state of order (low
entropy) to a state of maximum disorder (high
entropy)
 Entropy of a gas is greater than that of a liquid;
entropy of a liquid is greater than that of a solid
 Solids=low entropy; plasma=high entropy
 Entropy tends to increase when temperature
increases
 As substances change from one state to another,
entropy may increase or decrease
Le CHATELIER’S PRINCIPLE
 Anytime stress is placed on a system, the
sytem will readjust to accommodate that stress
 If a chemical system at equilibrium experiences
a change in concentration, temperature,
volume, or total pressure, then the equilibrium
shifts to partially counteract the imposed
change
 Can be used to predict the effect of a change in
conditions on a chemical equilibrium
 Is used by chemists in order to manipulate the
outcomes of reversible reactions, often to
increase the yield of reactions
Le CHATELIER’S PRINCIPLE
 When liquids are heated (stress) they
produce vapor particles (adjust)
 When liquids are cooled (stress) the
particles inside tighten to form a solid
(adjust)
Le CHATELIER’S PRINCIPLE
 Le Chatelier’s Principle explaining boiling and
condensation using covered beaker partially filled with
water
 At a given temperature the covered beaker constitutes a
system in which the liquid water is in equilibrium with the water
vapor that forms above the surface of the liquid.
 While some molecules of liquid are absorbing heat and
evaporating to become vapor, an equal number of vapor
molecules are giving up heat and condensing to become
liquid.
 If stress is put on the system by raising the temperature, then
according to Le Châtelier's principle the rate of evaporation will
exceed the rate of condensation until a new equilibrium is
established
PHASE DIAGRAMS
 A diagram showing the conditions at
which substance exists as a solid, liquid,
or vapor
 Shows the temperature and pressure
required for the 3 states of matter to exist
 Conditions of pressure and temperature
at which two phases exist in equilibrium
are indicated on a phase diagram by a
line separating the phases
 Draw the phase diagram for water
PHASE DIAGRAM-WATER
PHASE DIAGRAM-WATER
 Explanation of Phase Diagram:
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X axis-Temperature (°C)
Y axis- Pressure (kPa)
Line AB – line of sublimation
Line BD – boiling point line
Line BC – melting point line
Point B – triple point (all 3 states of matter
exist at the same time)
 Tm – melting point at standard pressure
 Tb – boiling point at standard pressure
HEAT in CHANGES of
STATE
 Energy Diagrams (also referred to as
Heating Curves)
 Graphically describes the enthalpy (the heat
content of a system at sonstant pressure)
changes that take place during phase
changes
 X axis is Energy (Heat supplied)
 Y axis is Temperature
HEAT in CHANGES of
STATE
 Constructing Energy Diagrams
 Step 1: Determine/Identify the melting and boiling
points for the specified substance
 Step 2: Draw x and y axis (energy vs temp)
 Step 3: Calculations
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First diagonal line: Q = mcDT
First horizontal line: Q = mHf
Second diagonal line: Q = mcDT
Second horizontal line: Q = mHv
Third horizontal line: Q = mcDT
Add up all values!!!
 Draw the energy diagram for 10 grams of water
as it goes from –25°C to 140°C