1. Thermodynamics

2. In a liquid the particles are still joined but can move around
Solid
Liquid
Gas
In a solid the particles are packed side by side and cannot move. They vibrate when they are heated
In a gas the particles are not joined and can move around in straight lines and do not react with each other
In a liquid the particles are still joined but can move around

3. Solid Liquid Gas 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
Solids have a shape and a volume
Solids cannot be compressed

4. 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

5. Gas laws
Force
Applying a force on the are of this piston will apply a pressure on the gas inside

6. Gas laws Increasing the pressure results in a decrease in volume
The volume decreases at the same rate as the pressure increases
Force

7. Pressure x volume is a constant (always the same figure)
Gas laws
Mathematically
Pressure x volume is a constant (always the same figure)
P X V = K
P1 x V1 = P2 x V2 = K
Force
This is called Boyle’s Law

8. 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

9. Gas Laws
When 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

10. Gas Laws
When the gas particles are heated to a higher temperature they have more kinetic energy and move about faster occupying a larger volume

11. When the temperature increases the volume increases
Gas Laws
When the temperature increases the volume increases
V= K T

12. Gas Laws
If the gas is heated and the volume cannot increase (in a closed container) the pressure increases
P = K T

13. Combining the three laws we get
Gas Laws
Combining the three laws we get
P x V = K T

14. Gas Laws
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
P1 x V = T1
P2 x V2 T2

15. Always use the Kelvin tEmperature scale in your calculationsoC
KELVIN
273 20
293 40
313 60
333 80
353
100
373
-273

16. Remember to change temperature to Kelvin
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

17. Gas Laws Example (Pressure stay constant)
V = T1 V2 T2
1.2 T2 =
295

18. Gas Laws Example =
295K
1.2 T2
295K x 1.2 2
T =
T = 177K ( -96oC)

19. 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.

20. This time temperature stays the same
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

21. 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

22. Gas Laws Example (Pressure stay constant)
P1 x V = T1
P2 x V2 T2
P2 x 1
573
1 x 5
293 =

23. Gas Laws Example (Pressure stay constant)
P1 x V = T1
P2 x V2 T2
1 x 5 x 573
293 x1 = P2
= bar