Gas Laws and Ideal Gases 1

7/24/2019 Gas Laws and Ideal Gases 1

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Topic 3 Thermal physics


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The kinetic theory of gases and the

gas laws


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Kinetic theory/ideal gas

We can understand the behaviour of

gases using a very simple model, that of

an ideal gas!

The model makes a

few simple assumptions"


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#deal gas assumptions

$ The particles of gas %atoms or molecules&

obey 'ewton(s laws of motion!

)ou should know theseby now*


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$ The particles in a gas move with a range

of speeds


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$ The volume of the individual gas particles

is very small compared to the volume of

the gas%or the volume of the container&


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$ The collisions between the particles and

the walls of the container and between the

particles themselves are elastic %no kinetic

energy lost&


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$ There are no forces between the particles

%e+cept when colliding&! This means that

the particles only have kinetic energy%no

potential&o you remember what internal

energy is-


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$ The duration of a collision is small

compared to the time between collisions!


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.ressure reminder

.ressure is defined as the normal

%perpendicular& force per unit area

. 0 1/

#t is measured in .ascals, .a %'!m2&


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.ressure reminder

What is origin of the pressure of a gas-


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.ressure reminder

4ollisions of the gas particles with the side

of a container give rise to a force, which

averaged of billions of collisions per

second macroscopically is measured as

the pressure of the gas

4hange of

momentum


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The behaviour of gases


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The behaviour of gaseshttp5//phet!colorado!edu/sims/ideal2gas/gas2properties!6nlp

When we heat a gas at constant volume,

what happens to the pressure- Why-

7et(s do it* )es, 6ust

not today" am sorry

for bursting your

bubble! 8a 8a
http://phet.colorado.edu/sims/ideal-gas/gas-properties.jnlphttp://phet.colorado.edu/sims/ideal-gas/gas-properties.jnlp


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The behaviour of gaseshttp5//phet!colorado!edu/sims/ideal2gas/gas2properties!6nlp

When we heat a gas at constant volume,

what happens to the pressure- Why-

. 9 T%if T is in

Kelvin&
http://phet.colorado.edu/sims/ideal-gas/gas-properties.jnlphttp://phet.colorado.edu/sims/ideal-gas/gas-properties.jnlp


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When we compress

%reduce the volume&

a gas at constant

temperature, what

happens to the

pressure- Why-

7et(s do it*


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When we compress

%reduce the volume&

a gas at constant

temperature, whathappens to the

pressure- Why-

p: 0 constant


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When we heat a gas a constant pressure,

what happens to its volume- Why-


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When we heat a gas a constant pressure,

what happens to its volume- Why-

: 9 T %if T is in

Kelvin&


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;+plaining the behaviour of

gases#n this way we are e+plaining the

macroscopicbehaviour of a gas %the


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The gas laws

We have found e+perimentally that"

t constant temperature, the pressure of

a fi+ed mass of gas is inversely

proportional to its volume!

p 9 =/: or p: 0 constant

This is known as >oyle(s law


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The gas laws

t constant pressure, the volume of afi+ed mass of gas is proportional to its

temperature"

: 9 T or :/T 0 constantThis is known as 4harle(s law

If T is in Kelvin


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The gas laws

t constant volume, the pressure

of a fi+ed mass of gas is

proportional to its temperature"

p 9 T or p/T 0 constant

This is known as the .ressure law

If T is in Kelvin


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The ey combining these three laws

p: 0 constant

:/T 0 constant

p/T 0 constant

We get p:/T 0 constant

?rp=:= 0 p: T= T

Remember, T

must be inKelvin


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n e+ample

t the top of @ount ;verest the temperature is

around ABK, with atmospheric pressure around

3!3 + =BC.a! t seas level these values are

3BBK and =!B + =BA

.a respectively! #f thedensity of air at sea level is =! kg!m23, what is

the density of the air on @ount ;verest-

.hysics, .atrick 1ullick, 8einemann


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n e+ample

t the top of @ount ;verest the temperature is around ABK, with atmosphericpressure around 3!3 + =BC.a! t seas level these values are 3BBK and =!B + =BA.arespectively! #f the density of air at sea level is =! kg!m23, what is the density of the airon @ount ;verest-

Take =kg of air at sea level

:olume 0 mass/density 0 =/=! 0 B!D3 m3!

Therefore at sea level

p=0 =!B + =BA.a, :=0 B!D3 m3, T=0 3BBK!


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n e+ample

t the top of @ount ;verest the temperature is around ABK, with atmospheric

pressure around 3!3 + =BC.a! t seas level these values are 3BBK and =!B + =BA.a

respectively! #f the density of air at sea level is =! kg!m23, what is the density of the air

on @ount ;verest-

Therefore at sea level

p=0 =!B + =BA.a, :=0 B!D3 m3, T=0 3BBK!

t the top of @ount ;verest

p0 3!3 + =BC.a, :0 - m3, T=0 ABK!


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n e+ample

t the top of @ount ;verest the temperature is around ABK, with atmosphericpressure around 3!3 + =BC.a! t seas level these values are 3BBK and =!B + =BA.arespectively! #f the density of air at sea level is =! kg!m23, what is the density of the airon @ount ;verest-

Therefore at sea level p=0 =!B + =BA.a, :=0 B!D3 m3, T=0 3BBK!

t the top of @ount ;verest p0 3!3 + =BC.a, :0 - m3, T=0 ABK!

p=:=/T=0 p:/T

%=!B + =BA.a + B!D3 m3&/3BBK 0 %3!3 + =BC.a + :&/ABK

:0 != m3,

This is the volume of =kg of air on ;verest

ensity0 mass/volume 0 =/!= 0 B!CD kg!m23!


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p: 0 constant

T


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The e


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Hample for more


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Hample iploma A th;dition


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Hample


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Muestions*

.age =D=

Muestions , C, , L

.age =D

Muestions =, =3, =N!

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Gas Laws and Ideal Gases 1