materi kinetic theory
TRANSCRIPT
Chapter 8
Chapter 8
Kinetic Model of Matter
Kinetic Model of Matter
Matter is made up of tiny particles called atoms and molecules. These particles are much too
small to be seen by naked human eyes. How do we prove their existence?
Matter is made up of tiny particles called atoms and molecules. These particles are much too
small to be seen by naked human eyes. How do we prove their existence?
contentscontents
States of Matter
Brownian Motion
Molecular Model of the Three States of Matter
Effects of Temperature
Pressure Exerted by a Gas
Chapter Review
States of Matter
Brownian Motion
Molecular Model of the Three States of Matter
Effects of Temperature
Pressure Exerted by a Gas
Chapter Review
SolidSolid LiquidLiquid GasGas
Fixed shape No fixed shape• can flow• take the shape of
container
No fixed shape• can flow• spread easily to fill
any vessel • take the shape of
vessel
Fixed volume Fixed volume No fixed volume• take the volume of
vessel
Not compressible Not compressible Highly compressible
Hard and rigid• large force
required to change its shape
Definite surface No surface
states of matterstates of matter
The kinetic theory of matter states that all matter is made up of a large number of tiny atoms
or molecules which are in continuous motion.
kinetic molecular model of matterkinetic molecular model of matter
states of matterstates of matter
brownian motionbrownian motion
dotted lines represent the path of smoke particles
between collision
kinetic molecular model of matterkinetic molecular model of matter
Using a microscope, smoke particles can be seen moving continuously and haphazardly, as a result of being hit by unseen fast-moving air molecules.
Using a microscope, smoke particles can be seen moving continuously and haphazardly, as a result of being hit by unseen fast-moving air molecules.
Brownian motion provides evidence for the kinetic molecular model of matter (kinetic theory of matter).Brownian motion provides evidence for the kinetic molecular model of matter (kinetic theory of matter).
Brownian MotionBrownian Motion
Fig. shows a smoke cell and the erratic path followedby a particle of smoke.
(continue on next slide)
Brownian MotionBrownian Motion
Applets illustrating Brownian motion
• http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=41
Explain what causes Brownian motion
• When the air molecule collide with a smoke particle– The molecules exert a force on the
smoke particle– Continuous random collisions produce a
random resultant force on the smoke particle
– Cause the smoke particle to move randomly and continuously.
Why is a microscope necessary in order to observe Brownian
motion?• The points of light are too faint to be
seen by an unaided eye• The small size particles are too small
to be seen with the naked eye.
Explain how Brownian motion provides evidence for the kinetic molecular model of matter
• Brownian motion is observed by suspending small sized particles in a fluid.
• Points of light are light scattered by the small-sized particles.
• The random, continuous and jerky movement of the smoke particles suggests that – the small sized particles are continuously
bombarded by random and continuously moving air particles or molecules.
brownian motionbrownian motion
If heat is supplied, the motion of the smoke particles becomes more vigorous.
The smaller the smoke particles, the more rapid is their motion.
Diffusion is a result of Brownian motion.
If heat is supplied, the motion of the smoke particles becomes more vigorous.
The smaller the smoke particles, the more rapid is their motion.
Diffusion is a result of Brownian motion.
smoke particles moving continuously and haphazardly (irregular or random motion)
diffusiondiffusion
Diffusion is the spreading of molecules of their own accord without any external aid.
Gas molecules move randomly all the time and they move into any available space. Hence they stay mixed and do not separate out.
Diffusion is the spreading of molecules of their own accord without any external aid.
Gas molecules move randomly all the time and they move into any available space. Hence they stay mixed and do not separate out.
brownian motionbrownian motion
diffusiondiffusion
Rate of diffusion depends onRate of diffusion depends on
temperature of gases: higher temperature leads to faster diffusion
density of gases: greater density leads to slower diffusion
temperature of gases: higher temperature leads to faster diffusion
density of gases: greater density leads to slower diffusion
diffusion in airdiffusion in air
brownian motionbrownian motion
If bromine vapour is released into a similar space full of airIf bromine vapour is released into a similar space full of air
bromine molecules keep hitting air molecules which get in the way
bromine vapour spreads quickly throughout the space but much slower than in vacuum
bromine molecules keep hitting air molecules which get in the way
bromine vapour spreads quickly throughout the space but much slower than in vacuum
bromine vapour
contained
bromine vapour diffused
vacuum
diffusion in liquiddiffusion in liquidDiffusion also takes place in liquids, at a very much slower rate.Diffusion also takes place in liquids, at a very much slower rate.
copper(II) sulphate solution and water become uniformly mixed after a while due to diffusion
copper(II) sulphate solution and water become uniformly mixed after a while due to diffusion
lidwater
copper (II) sulphate solution
copper (II) sulphate solution
diffusion of copper (II) sulphate solution in water
single uniform
layer
brownian motionbrownian motion
Why does diffusion occur?
• Because all molecules have spaces between them– And the molecules have some form of
random motion as stated in kinetic theory (all matter contains small atoms or molecules which are in random, continuous motion)
the molecular modes of the three states of matter
the molecular modes of the three states of matter
molecular structure of a solid
molecular structure of a liquid
molecular structure of a gas
molecular structure of solids, liquids and gasesmolecular structure of solids, liquids and gases
the molecular modes of the three states of matter
the molecular modes of the three states of matter
molecular structure of solids, liquids and gasesmolecular structure of solids, liquids and gases
SolidSolid LiquidLiquid GasGas
Forces Forces between between
moleculesmolecules
• balanced forces which hold molecules in fixed positions
• forces as strong as those in solid
• molecules not held in fixed position, move among one another throughout liquid
• negligible• only at moments
of collision, the intermolecular forces act
Distances Distances between between
moleculesmolecules
• arranged close together in a regular pattern
• not arranged in a regular pattern
• slightly further apart than in solid
• far apart• mainly empty
space between molecules
the molecular modes of the three states of matter
the molecular modes of the three states of matter
molecular structure of solids, liquids and gasesmolecular structure of solids, liquids and gases
SolidSolid LiquidLiquid GasGas
Motion of Motion of moleculesmolecules
• vibrate about fixed positions
• alternately attracting and repelling one another
• vibrate to and fro• alternately
attracting and repelling one another
• move randomly with high speed, colliding with one another and with the walls of the containers
Compress-Compress-ionion
• cannot be compressed
• molecules are arranged close together
• little space between them
• cannot be compressed
• molecules are still close together
• little space between them
• can be easily compressed
• far apart• mainly empty
space between molecules
the molecular modes of the three states of matter
the molecular modes of the three states of matter
molecular structure of solids, liquids and gasesmolecular structure of solids, liquids and gases
SolidSolid LiquidLiquid GasGas
When When heatedheated
• molecules gain energy and vibrate more
• separation between molecules increases slightly (solid expands)
• molecules vibrate and move about more vigorously
• separation between molecules increases slightly (liquid expands)
• move even more randomly with higher speed, colliding with one another and with the walls of the containers (gas expands a lot)
Applets illustrating kinetic theory
• http://intro.chem.okstate.edu/1314F00/Laboratory/GLP.htm
effects of temperatureeffects of temperature
As temperature increases, As temperature increases,
relationship between the motion of molecules and temperaturerelationship between the motion of molecules and temperature
surrounding air particles move faster and hit the particles move frequently and harder
Brownian motion of the smoke particles in the air becomes more vigorous
thermal energy is transferred to the molecules and the molecules gain kinetic energy causing molecules to move faster
surrounding air particles move faster and hit the particles move frequently and harder
Brownian motion of the smoke particles in the air becomes more vigorous
thermal energy is transferred to the molecules and the molecules gain kinetic energy causing molecules to move faster
• The pressure of a gas is causes by collisions of the molecules with the walls of the container.
• The magnitude of the pressure is related to how hard and how often the molecules strike the wall.
• The "hardness" of the impact of the molecules with the wall will be related to the velocity of the molecules times the mass of the molecules.
pressure exerted by a gaspressure exerted by a gas
pressure exerted by a gaspressure exerted by a gas
Pressure exerted by gas molecules increases due to:Pressure exerted by gas molecules increases due to:
relationship between the motion of molecules and pressurerelationship between the motion of molecules and pressure
a decrease in volume of a container, or (and)
an increase in temperature
a decrease in volume of a container, or (and)
an increase in temperature
pressure exerted by a gaspressure exerted by a gas
pressure of a gas in terms of motion of its moleculespressure of a gas in terms of motion of its molecules
1. Number of gas molecules per cm3
doubles
half the volume of container
2. Number of collisions of molecules with the wall in one second doubles
3. Pressure doubles
1. Molecules move faster
temperature of gas in container increases
2. Molecules hit the walls more frequently and more violently (with greater force)
3. Pressure increases
Relationship between Pressure, volume and Temperature
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Questions Questions
• A syringe contains 80cm3 of trapped air at room temperature. The piston is slowly pushed inwards, compressing the air. Some information about the air inside the syringe is given in the table below. Calculate the pressure P of the air after compression.
Before compression After compression
Volume of air
80 cm3 20 cm3
Temperature of air
25C 25C
Pressure of air
1.0 x 105Pa P
Questions
• The volume of air in the pump at the start of the stroke is 20 cm 3, and the pressure of the air is 1.00 x 105 Pa. Calculate the pressure when the volume has been reduced to 8 cm 3, assuming that no air has escaped from the pump and the temperature of the air is constant.
Matter Matter
SolidSolid GasGas
(a) Properties of solids, (a) Properties of solids, liquids and gasesliquids and gases
(b) Relationship between(b) Relationship betweenthe motion of molecules the motion of molecules and temperatureand temperature
(c) Pressure of a gas(c) Pressure of a gas
LiquidLiquid
(a)(a) Brownian motionBrownian motion(b)(b) diffusiondiffusion
Kinetic theory of matterKinetic theory of matter
is based on evidence likeis based on evidence like
consists ofconsists of
are discussed inare discussed in
used to explainused to explain