THERMODYNAMICS. Solid Liquid Gas In a solid the particles are packed side by side and cannot move....
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Transcript of THERMODYNAMICS. Solid Liquid Gas In a solid the particles are packed side by side and cannot move....
![Page 1: THERMODYNAMICS. Solid Liquid Gas In a solid the particles are packed side by side and cannot move. They vibrate when they are heated In a liquid the particles.](https://reader038.fdocuments.in/reader038/viewer/2022110319/56649c765503460f9492a370/html5/thumbnails/1.jpg)
THERMODYNAMICS
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Solid
Liquid Gas
In a solid the particles are
packed side by side and cannot
move. They vibrate when they
are heated
In a liquid the particles are
still joined but can move around
In a gas the particles are not joined and
can move around in straight lines and do not react with each
other
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Solid
Liquid Gas
Solids have a shape and a
volumeSolids cannot be
compressed
Liquids do not have a shape
but have a volume
Liquids cannot be compressed
Gases do not have shape or volume, they can spread out and fill
the shape they are contained in
Gases can be compressed
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GAS LAWS
Compression (increasing pressure) is caused by exerting a force on an area
Pressure = Force N/m2 (Pascals)
Area
Increasing force on the same area means increasing pressure
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GAS LAWS
Force
Applying a force on the are of this piston will apply a pressure on the
gas inside
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GAS LAWS Increasing the pressure results in
a decrease in volume
The volume decreases at the same rate as the
pressure increases
Force
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GAS LAWS MathematicallyPressure x volume is
a constant (always the same figure)
P X V = KP1 x V1 = P2 x V2 = K
Force
This is called Boyle’s Law
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EXAMPLE
If the gas in a cylinder has a volume of 4m3 at a pressure of 4 N/m2 What will the volume be if the
pressure is increased to 8 N/m2 ?
P1 x V1 = P2 x V2 = K
4 x 4 = 8 x V2 = 16
V2 = 16 ÷ 8 = 2m3
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GAS LAWSWhen the gas
particles are at a low temperature they have a low
amount of kinetic energy and are not moving about very much and do not
occupy much volume
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GAS LAWSWhen the gas particles are
heated to a higher temperature they have more kinetic energy and move
about faster occupying a larger
volume
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GAS LAWS
When the temperature increases the volume increases
V= K T
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GAS LAWS
If the gas is heated and the volume cannot increase (in a closed
container) the pressure increases P = K
T
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GAS LAWS
Combining the three laws we get
P x V = K T
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GAS LAWS
P1 x V1 = T1
P2 x V2 T2
A gas has a constant pressure, temperature and volume, if one of the quantities
changes and another stays constant the third will change to compensate
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ALWAYS USE THE KELVIN TEMPERATURE SCALE IN YOUR CALCULATIONS
oC KELVIN
0 273
20 293
40 313
60 333
80 353
100 373
-273 0
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GAS LAWS EXAMPLE
The temperature of 2m3 of air is 22oC. It is compressed to a volume of 1.2m3 whilst being kept at a constant pressure of 1 bar. Calculate
the final temperature of the air.
Remember to change temperature to Kelvin
22oC = 295K
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GAS LAWS EXAMPLE (PRESSURE STAY CONSTANT)
V1 = T1
V2 T2
2 = 295
1.2 T2
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GAS LAWS EXAMPLE
2 = 295K
1.2 T2
T2 =295K x 1.2
2
T2 = 177K ( -96oC)
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GAS LAWS EXAMPLE
Dry steam is compressed isothermally from a pressure of 1 bar to a pressure
of 10 bar. The initial volume of the steam is 2m3. Calculate the volume of
the steam after compression.
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GAS LAWS EXAMPLE This time temperature stays the same
So P1V1 = P2V2
1 x 2 = 10 x V2
V2 = 1 x 2 = 0.2m3
10
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GAS LAWS EXAMPLE
An air compressor operates with a compression ratio of 5:1. If the air is at a pressure of 1 bar and a
temperature of 20oC before compression and the temperature after compression is 300oC. What will
the final pressure be?
V1 = 5 V2 = 1
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GAS LAWS EXAMPLE (PRESSURE STAY CONSTANT)
P1 x V1 = T1
P2 x V2 T2
1 x 5 293
P2 x 1 573
=
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GAS LAWS EXAMPLE (PRESSURE STAY CONSTANT)
P1 x V1 = T1
P2 x V2 T2
1 x 5 x 573 293 x1
P2= = 9.8 bar