5.19 Boyle's Law

5.19 Boyle's Law

· 5.19 use the relationship between the pressure and volume of a fixed mass of gas at constant temperature:

p1V1 = p2V2

p1 = Pressure at the beginning [kPa, bar or atm]

V1 = Volume at the beginning [m3 or cm3]

p2 = Pressure at the end [kPa, bar or atm]

V2 = Volume at the end [m3 or cm3]

(Note: can use any units for V and p as long as they are the same at the beginning and end)

5.19 Boyle's Law demos

Fun with the vacuum pump!
· Marshmellows
· Food colouring in pipettes
· Surgical gloves

5.19 Ideal graph and conclusion

5.19 Questions

PFY, p.36, Q.1a, 3 and 4
1) Boyle's Law: for a "constant" mas of gas, at constant "temperature", "pressure" x "volume" is constant. Pressure is "inversely" proportional to "volume"

3) P(1)T(1) = P(2)V(2)
4 x 1 = 1 x V(2)
V(2) = 4cm^3

4) P(1)V(1) = P(2)V(2)
1 x 60 = P(2) x 40
P(2) = 1.5 atm

Extension: PFY, p.36, Q.5.
5)

P(1)V(1) = P(2)V(2)
2.5 x 1000 = 1 x V(2)
V(2) = 2500 cm^3

Pressure in tyre and pump = 1atm
Volume of Tyre + pump = 1000+100 = 1.100cm^3
Volume of Tyre (without the pump) = 1,000 cm^3

1,100 x 1 = 1,000 x P(2)
P(2) = 1.1 atm

See the full gallery on Posterous

5.19 Experiment

5.19 Experiment

· Change the pressure of a fixed mass of gas at a constant temperature
· Measure the volume
· Use the EXCEL spreadsheet to analyse your results

See the full gallery on Posterous

5.18

5.17 Demo
Cloud formation
· Place a little water in the bottom of a 1½ litre plastic bottle
· Squeeze a few times
· Introduce a small amount of smoke
· Squeeze and release several times
· When you squeeze, the cloud disappears; when you release, the cloud reforms

Explanation
· When the pressure increases the temperature increases and vica versa
· The smoke particles are nucleating sites on which the water can condense

5.18 Gay-lussac's law

· 5.18 use the relationship between the pressure and Kelvin temperature of a fixed mass of gas at constant volume:

p1 / T1 = p2 / T2

p1 = Pressure at the beginning [kPa, bar or atm ]

T1 = Absolute temperature at the beginning [K]

p2 = Pressure at the end [kPa, bar or atm]

T2 = Absolute temperature at the end [K]

(Note: the units of temperature must be Kelvin, not oC! The units of pressure can be any, as long as the same at the beginning and the end)

5.18 Ideal graph and conclusion

5.18 Question

Collins, p.116

a. If we cool the gas in a rigid, sealed tin can, what happens to the pressure inside the can? (1 mark)
The pressure decreases.
b. Explain your answer to part a. by using the Kinetic Theory (4 marks)
The decrease in temperature results to the decrease in the average kinetic energy of the particles. This results to the decrease in the speed of the particles so they collide with less force and less frequently on the walls of the container. There is less force exerting on the wall resulting to the decrease in pressure.

+ The volume remains the same throughout since the tin can is a rigid container.

See the full gallery on Posterous

5.18 Gay-lussac's law

5.18 Gay-lussac's law

· 5.18 use the relationship between the pressure and Kelvin temperature of a fixed mass of gas at constant volume:

p1 / T1 = p2 / T2

p1 = Pressure at the beginning [kPa, bar or atm ]

T1 = Absolute temperature at the beginning [K]

p2 = Pressure at the end [kPa, bar or atm]

T2 = Absolute temperature at the end [K]

(Note: the units of temperature must be Kelvin, not oC! The units of pressure can be any, as long as the same at the beginning and the end)

5.18 Ideal graph and conclusion

See the full gallery on Posterous

5.16

5.16

Answers
1. What variable remains constant for this experiment?

Volume

2. Explain in terms of the particles what happened to the pressure when the temperature increased

When the temperature is increased, the average kinetic energy increases. Therefore, the particles hit the walls of the container with a greater force and more frequently. This increases the pressure.

3. Is the temperature proportional to the average speed? Justify your answer

No; the line on the graph is not straight.

4. Is the temperature proportional to the average kinetic energy of the particles? Justify your answer

Yes; the graph of temperature against the [average speed of the particles^2] is a straight line.

5. Why is the word 'average' used?

Each particle in the container has different speeds and therefore, there is a range of kinetic energies but, on average, T α KE.

See the full gallery on Posterous

5.14

5.14
· 5.14 describe the Kelvin scale of temperature and be able to convert between the Kelvin and Celsius scales

Converting Centigrade to Kelvin
TK = ToC + 273

Converting Kelvin to Centigrade
ToC = TK - 273

TK = Temperature in Kelvin [K]

ToC = Temperature in Degrees Centigrade [oC]

5.14 Questions
· Collins p.118

Q1) Absolute zero is the lowest temperature possible where there is no heat in the particles to make it have kinetic energy. This means that at this temperature, -273 oC, the particles stop moving completely and do not even vibrate. If you go beyond absolute zero, there will be no change and nothing will happen. Q2)
a)
i) Tk = Toc + 273
Tk = 293 K
ii) Tk = Toc + 273
Tk = 423 K
iii) Tk = Toc + 273
Tk = 1273 K

b)
i) Toc = Tk - 273
Toc = 27 oC
ii) Toc = Tk - 273
Toc = 377 oC
iii) Toc = Tk - 273
Toc = 727 oC

PhET Gas Properties Simulation

<div style="position: relative; width: 300px; height: 228px;"><a href="http://phet.colorado.edu/sims/ideal-gas/gas-properties_en.jnlp" style="text-decoration: none;"><img src="

" alt="Gas Properties" style="border: none;" width="300" height="228"/><div style="position: absolute; width: 200px; height: 80px; left: 50px; top: 74px; background-color: #FFF; opacity: 0.6; filter: alpha(opacity = 60);"></div><table style="position: absolute; width: 200px; height: 80px; left: 50px; top: 74px;"><tr><td style="text-align: center; color: #000; font-size: 24px; font-family: Arial,sans-serif;">Click to Run</td></tr></table></a></div>

5.13

5.13 Starter
· How can you fit a giraffe, 2 dogs and a swan into a standard laboratory beaker?!

5.13 Starter 2

· Use particle theory to explain why the gas in the balloon contracts

Explanation
· The temperature of the gas inside the balloon decreases so the average speed of the particles decreases
· Consequently the gas particles collide with the walls of the balloon with less force and less collisions per second
· Because the walls of the container are flexible, the volume decreases

5.13 Charles' law

· 5.13 understand that there is an absolute zero of temperature which is –273oC

Open the Charles' law interactive experiment
· Adjust the temperature
· What’s the relationship between temperature and volume?
· Plot a graph of V against T
· Take a screen shot of the graph

5.13 results and conclusion

28 October 2011

Conclusion
· Volume is directly proportional to absolute (Kelvin) temperature
· V α T

Charles' law interactive experiment.swf Download this file

See the full gallery on Posterous

5.11

5.11 Starter

· You're looking at smoke particles in air under a microscope
· They appear to be jiggling about
· Why?

· (Don't worry if you can't work this out straight away - Albert Einstein was the bloke who eventually explained what's happening here!)

5.11
· 5.11 understand the significance of Brownian motion

Model 1
· What does the red puck represent?
· What do the metal balls represent?

Model 3
· What do the "smoke" particles look like?
· Why are they moving?
· What do the "air" particles look like?

5.11 explained

Model 1
· What does the red puck represent?
o The large, visible smoke particle
· What do the metal balls represent?
o The small, not visible air particles

Model 2
· What do the small red particles represent?
o The small, not visible air particles
· What does the large blue particle represent?
o The large, visible smoke particle
· What does the view on the left of the screen represent?
o The view through the microscope lense
· Why can‘t you see the red particles in this view?
o They are too small to see

Model 3
· What do the "smoke" particles look like?
o They are the 5 large, sand coloured particles
· Why are they moving?
o Small, fast moving air particles are colliding with the smoke particles and making them move
· What do the "air" particles look like?
o They are the numerous, small, white particles

5.11 Questions

1. Draw the path of a smoke particle in air (3 marks)
-There must be arrows on the path
-The angle between the paths have to be random
-The path lengths between collisions are random
2. Explain what is meant by Brownian Motion of smoke particles in air and how it provides evidence for air particles (4 marks)
-Large smoke particles are visible
-Since air particles are smaller, we cannot see them
-The smoke particles move because of the air particles collide with them
-Therefore, the movement of smoke particles is proof that air particles exist
3. What change would you expect to see in the movement of the smoke particles if the air was cooled down? Why? (2 marks)
-The smoke particles would move slower
-A lower temperature in air would mean that the air particles would move slower and collide with the smoke particles with less force. This makes the spoke particles move slower.

brownian_motion.swf Download this file

See the full gallery on Posterous

5.12+5.15

5.12+5.15 Starter

Questions
· Why does the needle on the meter move when gas particles are introduced into the box?
· What does the meter measure?

Answers
· The gas particles collide with all of the walls of the container. The wall on the right moves outwards and moves the needle.
· Pressure. The gas particles colliding with the walls makes a force on the walls. The walls have a surface area so the quantity measured is pressure, p=F/A.

5.12+5.15 Questions
· 5.12 recall that molecules in a gas have a random motion and that they exert a force and hence a pressure on the walls of the container
· 5.15 understand that an increase in temperature results in an increase in the speed of gas molecules

Try the animation http://www.lon-capa.org/~mmp/kap10/cd283.htm

1. How do the particles create a pressure? The particles create a pressure by colliding with the wallsof the container
2. If you increase the temperature, how does the movement of the particles change? The average kinetic energy (the average speed) of the particles will increase.
3. If you increase the temperature, how does the number of collisions per second change? If you increase the temperature, the number of collisions per second increases.
4. If you increase the temperature, what does this do to the pressure? If the temperature increases, the pressure increases.

5.12+5.15 Plenary

Ideal gases - summary of terms.pptx Download this file