IDEAL GASES

Question 1

1. What is the atmosphere composed of?

Answer 1

• Nitrogen (N2)
• Oxygen (O2)
• Water Vapour
  (this depends on the local humidity levels)

Question 2

2. What are three properties of gases?

Answer 2

1. they are miscible
   (they mix together)
2. they form homogenous mixtures
3. they are compressible

Question 3

3. Why do water and oil not mix together when they are in a liquid state?

Answer 3

• oil is less dense than water
• it will rise above the water
• water is more dense than oil
• it will sink below the oil
• they have different intermolecular forces between
  their particles

Question 4

4. In which state do oil and water mix together?

Answer 4

• in a gaseous state

Question 5

5. What results in the properties of gases?

Answer 5

• the large distances between the gas particles
• this limits the interactions that are possible between
  the particles

Question 6

6. What is air composed of?

Answer 6

• 0.1% volume of gas particles
• 99.9% empty space

Question 7

7. How is gas pressure calculated mathematically?

Answer 7

• it is the force divided by the given area
• the units of force are Newtons
• the units of area are m²
• the units of pressure is Pascals (Pa)

Question 8

8. How else can Newtons be written?

Answer 8

• kg m / s²

Question 9

9. How else can Pascals (Pa) be written?

Answer 9

• N/m²
• kg / (ms²)
• pascals are an extremely small unit

Question 10

10. How would we work out the Gas pressure in this diagram?

• the column of the Earth’s atmosphere has a
  dimension of 1m x 1m
• this is estimated to have a mass of 10 300kg
• the column of gases is pressing down on the surface
  of the Earth at sea level
• this creates the atmospheric pressure
• the area of the column is 1.00m²

Answer 10

• P = m x g / A
• the gravitational force is calculated as F = m x g
• g = Earth’s gravitational constant
• g = 9.8m.s⎺²

∴P = 10 300 kg x 9.81m.s⎺² / 1.00m²

NB:
- if we go to a high mountain
- the height of the column is smaller
- this gives a reduced mass
- it also gives a reduced atmospheric pressure

Question 11

11. Why is Mercury harmful to your health?

Answer 11

• it is neurotoxic
• it destroys the neurons in oyur brain

Question 12

12. What is a Barometer?

Answer 12

• it is a weight measuring device
• it measures the weight of the atmospheric gases acting
  on the Earth
• it is a crude instrument
• it is used for measuring atmospheric pressures

Question 13

13. How do we set up a Mercury Barometer?

Answer 13

• we fill up a bowl with liquid mercury
• we fill a glass test tube completely with mercury
• we place the glass test tube with the opening facing
  downwards
• the test tube is placed inside the bowl with Mercury

Question 14

14. How does a Mercury Barometer work?

Answer 14

• gravity pulls down on the Mercury in the test-tube
• the mercury moves down the test tube
• this creates a vacuum at the top
• the atmospheric pressure is also pushing down on the
  liquid mercury in the bowl
• this pushes the liquid up into the test tube

Question 15

15. How do we express atmospheric pressure using a Mercury Barometer?

Answer 15

• when a balance is reached between the forces in the
  Mercury barometer
• the height of Mercury in the test tube is measured
• in this case it is 760mm
• this is the atmospheric pressure

Question 16

16. What is are other equivalent units of 1 atm?

Answer 16

• 760 mmHg
• 760 torr
• 101.325 kPa

Question 17

17. What is a torr?

Answer 17

• it is a unit of measurement
• it is equal to 1 mmHg

Question 18

18. What is one bar equal to?

Answer 18

• 100 kPa
• 0.986923 atm

Question 19

19. How do we calculate the pressure of an enclosed gas?

Answer 19

• using an open ended manometer

Question 20

20. What does an open-end manometer consist of?

Answer 20

• it has a glass bulb on the left side
• this is filled with an unknown gas
• it has a U shaped tube
• the U shaped tube is filled with Mercury
• the right side of the U-tube is open to the
  atmosphere

Question 21

21. How does an Open end Manometer work?

Answer 21

• the atmosphere is pushing down on the right side of
  the U-tube
• this is pushing the Mercury down
• the gas is pushing down on the mercury on the left
  side of the U-tube

Question 22

22. What happens when the gas pressure is equal to the atmospheric pressure in the Open End Manometer?

Answer 22

• the levels of the mercury in the two arms of the U-tube
  will be the same

Question 23

23. What happens when the gas pressure is less than the atmospheric pressure in the Open End Manometer?

Answer 23

• the right side of the U-tube will be lower than the left-
  side

Question 24

24. What happens when the gas pressure is more than the atmospheric pressure in the Open End Manometer?

Answer 24

• the left side of the U-tube will be lower than the right-
  side

Question 25

25. What determines the pressure that an enclosed gas exerts?

Answer 25

- the frequency of the collisions with the inner container walls - the intensity of these collisions

Question 26

26. What kind of motion do the gas particles inside the box have?

Answer 26

- constant motion - this type of motion is random - it is called Brownian motion

Question 27

27. What does the Brownian motion of these particles result in?

Answer 27

- the randomness of the motion results in continuous collisions between the gas particles - this leads to a redirection of these particles in different directions

Question 28

28. What creates pressure in this container?

Answer 28

- the gas particles collide frequently with the inner walls of the container - this creates pressure

Question 29

29. Which two factors determine the magnitude of the pressure inside the box?

Answer 29

1. THE FREQUENCY OF THE COLLISIONS - these happen with the inner walls of the box 2. THE INTENSITY OF THE COLLISIONS

Question 30

30. What happens when the frequency of the collisions of the particles is higher?

Answer 30

- the higher the pressure within the box will be

Question 31

31. What happens when the intensity of the collisions of the particles is higher?

Answer 31

- the higher the force of the collision - the pressure is higher

Question 32

32. What keeps a balloon from capsizing on itself?

Answer 32

- the collisions of the particles within the balloon - these collisions are caused by the Brownian motion of the particles

Question 33

33. What will happen to the pressure inside a container of gas if the temperature of the gas is increased?

Answer 33

A HIGHER TEMPERATURE RESULTS IN: - the particles moving faster - the particles have more kinetic energy - they collide with the walls of the container more frequently - they collide with the walls with more force - the total pressure inside the container increases

Question 34

34. What will happen to the pressure inside a container of gas if the container is reduced to half its volume?

Answer 34

A HALVED CONTAINER RESULTS IN: - the particles are moving at the same speed - they will collide with the walls of the container with the same force - they will travel a much shorter distance before they collide with the walls of the container - they will collide more frequently - the pressure will increase