Materi kinetic theory

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

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.


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.


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


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


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


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





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





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





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

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 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 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

2

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1

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T

VP

T

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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

Technology

Materi kinetic theory