Ideal Gases

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Ideal Gases

K Warne

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Gas Problems – Aerosol cans

Question: Pressurized containers (aerosol cans) carry warnings to avoid

heating the container.

Why is this?

Describe a gas law that relates to this problem and explain it’s relevance

in terms of the Kinetic Theory of Gases.

NO!!!!








Gas Problems• Explain how and why real gases differ from the behaviour

of an ‘ideal gas’.

Real gases deviate from the ideal gas model - this occurs at high pressure and low temperature.

1. At high pressure

• the particles are forced close together and their volume adds to the total volume of the gas.

• The volume of the real gas is larger than that of an ideal gas at high pressure.

2. At low temperature

• the forces between the particles pull them closer together.

• The volume of the real gas is therefore lower than that of an ideal gas.








Gas Problems1. If a car tyre has a pressure of 280 kPa at 25o C, what

would the pressure be if the tyre temperature heats up to

38o C on a long journey? (Assuming the volume stays

constant.)

P1 = P2

T1 T2

280000 = P2

298 311

P2 = 260906 Pa

= 292.21 kPa (4)








Temperature Scales• 0° Celsius = 273Kelvin

• ABSOLUTE ZERO 0

Kelvin = -273°C

• Celsius Kelvin

……………………

• Kelvin Celsius

…………………….

Convert to K:

Boiling point water 100o C

Room Temp 25o C

Body Temperature 37o

Kelvin Celsius Fahrenheit








Macroscopic / microscopicKinetic theory relates the ________________ properties of substances

to its ___________________ properties.

Pressure= force/area

Volume =lxb h

Temperature = o C or K

Pressure: _________________ per unit _________.

Temperature: is a measure of the _____________________ of particles.

Macroscopic properties:

___________, ___________, ____________

Microscopic properties:

________ & ________ of particles








Effect of Temperature - Guy Lussacs’ LawThe temperature of a fixed mass of gas is increased while the volume is kept

constant.

Guy Lussack's LawP (Pa) x103 T (K)

V = const

100 298.0

x1.4 120 357.6 x 1.4

140 417.2

160 476.8

180 536.4

x 2 200 596.0 x 2

The temperature is directly proportional to the pressure - if the pressure doubles the temperature

would also double.

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

0 50 100 150 200 250T

emp

era

ture

(K

)Pressure (Pa) x 103

T (K)







Effect of Temp








A weather balloon has a volume of 5 dm3 at sea level when the

temperature is 25o C. What would the volume of the balloon be if

the temperature rose to 35o C on a hot day?

Pressure - volume example.

Given: V1 = 5 dm3 T1 = 25 + 273 = 298 K T2 = 35 + 273 = 308K

Asked: V2

V1/ T1 = V2 /T2

(5/298) = V2 / 308

V2 = 308*(5/298) = 5.17 dm3








Pressure & VolumeIf the __________ of a fixed mass of gas is _______

the _________ will increase. (T = const.)

The pressure increases

because…This happens

because there is

________ for the

particles to

collide with so

the ______ of

__________

with the sides of

the container

_____________

increases.








Boyles Law

Spreadsheet

T = 298K

Volume vs Pressure for a fixed mass of gas (T = const)

10

15

20

25

30

35

40

45

50

55

55 75 95 115 135 155 175 195 215

Boyle's Law

Pressur

e (kPa)

Volume

(cm3)

200 15

150 17

118 21

96 27

80 35

69 42P 1/V

P = k (1/V)

pV = k






E:/Bergvliet Documents/Lessons/Grade 11/Boyle's Law.xls



Ideal Gas DeviationsReal gases deviate from the ideal gas model - this

occurs at __________________ and ___________________.

At high ___________________

• the particles are _____________ and their _____________ adds to the ____________ of the gas.

• The volume of the real gas is ______________than that of an ideal gas at high pressure.

P








Ideal Gas DeviationsAt low ______________

• the _____________ between the particles pull them ___________ together.

• The volume of the real gas is therefore __________ than that of an ideal gas.








Real Gases - Deviations Real gases deviate from ideal

behavior at low __________ and high ____________.

Many real gases ___________ under these conditions.

At low __ and low ___

Real gas particles are _______ ______ by attractive forces - they therefore exert _____ ___________.

Indicate these areas on the graph!








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Ideal Gases