1. Behavior of Gas Molecules
KINETIC MOLECULAR THEORY
and the ABCs of Gas Laws

2. Essential Question How do gases behave?
How do things like pressure, temperature and volume affect gases?
Can we perform gas stoichiometry?

3. Launch activity Take 5 minutes and fill in your chart:
What are some key characteristics of solids, liquids and gases in regards to spacing, potential of movement, and filling a container?

4. Launch Activity Use these questions to help you:
In which phase is there the least spacing?
In which phase is there the most potential for movement?
Which phase(s) do(es) not have a definite shape?

5. Launch activity Solid Liquid Gases Spacing Potential for movement
Filling a container

6. Behavior of gases How would you describe the behavior of gases?
How do they differ from solids and liquids?
How do the molecules interact with each other?
What happens if you keep filling a balloon?

7. Kinetic Molecular Theory
In 1860, Two scientists developed the Kinetic Molecular Theory to explain the behavior of gases and the relationship among pressure, volume, temperature and number of particles in a gas sample.
The theory describes particle size, motion and energy.

8. Kinetic Molecular Theory
It is called “kinetic” because the word kinetic means “to move”.
Objects in motion have kinetic energy!
Quick check – what is potential energy mean then?

9. Kinetic Molecular Theory
po·ten·tial en·er·gy
Noun
the energy possessed by virtue of position relative to others, stresses within itself, electric charge, and other factors.

10. Particle Size
Gases consist of small particles separated by empty space
The volume of the particles is so small in comparison to the empty space, we say…
The volume or size of the individual particles is negligible or equal to zero
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11. Particle Motion Gas particles are in constant, random motion.
Gas particles move in straight line (linear) motion until they collide with the boundary or with other gas particles
Collision between gas particles are elastic meaning no energy is lost.
Particles are assumed to NOT attract or repel each other

12. Kinetic Energy = ½ (mass) (velocity)2
Particle Energy
Since all of the molecules are in linear motion, and therefore have a velocity, they possess kinetic energy as defined by the following equation:
Kinetic Energy = ½ (mass) (velocity)2
KE = ½ mv2
Temperature is simply a measure of the average kinetic energy of the particles in a sample.

13. Behavior of gases In describing the behavior of gases, we talk about
Temperature
Volume
Pressure
Before we can learn to solve Gas Law problems, we must investigate these new three vocabulary words

14. TEMPERATURE Two scales to measure temperature: Celsius: Kelvin:
0°C - temperature at which water freezes
100°C - temperature at which water turns to gas
Kelvin:
O K - Absolute Zero where all motion stops!
273 K - temperature at which water freezes
373 K - temperature at which water turns to gas

15. TEMPERATURE CONVERSION
From Celsius → Kelvin
Add 273 degrees
40ºC = 313K
From Kelvin → Celsius
Subtract 273 degrees
248 K = - 25ºC
For gas law problems, we MUST use Kelvin in our calculations!

16. VOLUME Volume is defined as the space that matter occupies.
The base unit for volume is the liter
1 liter (L) = 1000 milliliters (mL)
1 milliliter (mL) = 1 cubic centimeter (cm3)
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17. PRESSURE
Pressure is defined as the amount of force applied to an area of matter:
Force
Pressure =
Area
Gas particles apply force on the container as particles collide with the boundary
The SI unit for pressure is the pascal (Pa) named after Blaise Pascal ( ) a French mathematician and philosopher.

18. Pressure There are many traditional units for pressure:
Newton per meter squared (N/m2)
Pressure per square inch (psi) – used for your tires!
Millimeters of mercury (mmHg) – from barometers
Torr – defined as the same as mmHg
Bar – often used in pressure gauges
Atmospheres (atm)
Since there are so many units, we need to CONVERT

19. Pressure Conversions Important pressure conversions
When doing these problems, be sure to be consistent with your pressure units!
1 atm = 101.3kPa
1 atm = 760 mmHg
1 atm = 760 torr
1 kPa = atm
1 kPa = mmHg
1 kPa = torr

20. STANDARD TEMPERATURES & PRESSURES (STP)
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21. Let’s practice
The pressure atop the world’s highest mountain, Mt Everest is usually about 33.6 kPa. Convert this pressure to atmospheres. How does this compare to the pressure at sea level?
0.33 atm
Sea level is 1.0 atm

22. Let’s practice
The atmospheric pressure in Denver, Colorado is usually about 84 kPa. What is this pressure in atm and torr units?
0.83 atm
torr

23. Check for understanding
Work with a partner on completing:
Let’s practice problems

24. The Gas Laws

25. Demo #1
Demo: Take a syringe and depress it to see how it feels. Now hold your finger over the end and depress again.
What happens?
What relationship can we draw between pressure and volume?

26. Demo #1
Now add a baby marshmallow to the syringe. Place the syringe at the farthest out positon. Cover with a cap or your finger and push the syringe in as far as you can. What happens to the marshmallow? Release your finger or the cap. What happens to the marshmallow? Now try it the opposite way!

27. Cartesian Diver Demo
A small amount of air is placed inside a pipette and sealed and placed inside the water bottle.
Squeezing the bottle (increases/decreases) the pressure inside the bottle.
As a result, the volume of air (increases/decreases) sending the diver down! (Density = mass/volume)

28. Gas Law Relationships What was the relationship between
Pressure Volume
This is called Boyles Law
In order to do this experiment, what did we not change – or hold constant?

29. Boyle’s Law
Examines the behavior of gas under the condition of constant temperature
As the volume containing gas particles is reduced, the particles are forced closer together.
Can be written as: P1V1 = P2V2
1 stands for initial conditions
2 stands for final conditions

30. Boyle’s Law is an Inverse Relationship
As Pressure ↑, Volume ↓
As Pressure ↓, Volume ↑
Boyle’s Law is an Inverse Relationship

31. Problems Let’s try some problems.
Before solving each problem, predict if your value will increase or decrease. Then solve. Check your answer to see if it agrees with your prediction!

32. Boyles Law problems
The gas in a 600 mL balloon has a pressure of 1.20 atm. If the temperature remains constant, what will be the pressure of the gas in the balloon when it is compressed to 400 mL?
1.8 atm

33. Boyles Law problems
2. An oxygen container has a volume of 48 mL and a pressure of 420 kPa. What is the volume of this gas when the pressure is 105 kPa? 192 ml

34. Boyles Law problems
3. A tank of compressed CO2 has a pressure of 850 psi and a volume of 150 mL. What is the volume of this gas when the pressure is 45 psi?
2,833 ml

35. Demo #2 Balloon and the Flask (or Hot Air Ballooning)
Place 10 mLs. or so of water in an Erlenmeyer flask. Stretch an un-inflated balloon over the mouth of the flask (250 mL. flask).
Place the flask on hot plate
What happens to the balloon? Why?

36. Demo #2 Now, put the flask in a beaker of ice and let it cool.
Now what does the balloon do? Why?

37. Gas Law relationships What was the relationship between
Temperature Volume
This is called Charles’ Law
In order to do this experiment, what did we not change – or hold constant?

38. Charles’ Law
Examines the behavior of gas under the condition of constant pressure
As the volume containing gas particles is reduced, the particles must move slower to exert the same force over a smaller surface area. or
As temperature is decreased, the particles would exert less force on the available surface area. In order to restore the pressure lost through this process, the surface area has to be reduced to compensate.

39. Temperature must be in KELVINS! Charles’ Law is a Direct Relationship
V V2 =
T T2
Temperature must be in KELVINS!
Charles’ Law is a Direct Relationship

40. Charles Law problems
A 240 mL sample of argon gas at 270 K is cooled until the volume is 180 mL. What is the new temperature?
202.5 K

41. Charles Law problems
2. A container of oxygen with a volume of 60 L is heated from 300 K to 400 K. What is the new volume? 80 L

42. Charles Law problems
3. When a piston with a volume of 35 mL is heated from 25ºC to 323ºC it expands. Assuming the pressure on the piston remains the same, determine the new volume of the cylinder.
70 mL

43. Demo #3
Fill a shallow dish with water (colored blue) Place two candles in the dish with water Cover with large beaker Look at the level of the water before and after the candles go out?

44. Gas Law Relationships What was the relationship between
Temperature Pressure
This is called Gay-Lussac’s Law
In order to do this experiment, what did we not change – or hold constant?

45. Gay-Lussac’s Law
Examines the behavior of gas under the condition of constant volume.
An increase in temperature increase the collision frequency and energy, thus increasing pressure.

46. Gay Lussac’s Law -------- = --------- T1 T2
P P2 =
T T2
Temperature must be in KELVINS
Gay Lussac’s Law is a Direct Relationship

47. Gay Lussac’s problems
Determine the pressure change when a constant volume of gas at 1.00 atm is heated from 20.0 °C to 30.0 °C.
1.03 atm

48. Gay Lussac’s problems
2. A gas has a pressure of atm at 50.0 °C. What is the pressure at standard temperature? 0.31 atm

49. Gay Lussac’s problems
3. A gas has a pressure of mm Hg at 40.0 °C. What is the temperature at standard pressure? 340 K

50. Teeter Totter
Is there a way we can easily remember all of these relationships?

51. Demo #4 Demo: Boil water inside a soda can; invert into a ice bath.
What happens?
What laws are we seeing in action?

52. Demo #4
According to Charles’ Law, as temperature inside the can rapidly decreases, the volume this air will proportionally reduce in volume.
According to Boyle’s Law, the water pressure on the outside wall of the can will assist the trapped air in reducing its volume by increasing the pressure and crushing the can.
Together, the laws are “combined”!

53. COMBINED GAS LAW
Combines all three gas laws and allows us to solve for changing conditions.

54. Combined Gas Law problems
A canister containing air has a volume of 85 cm3 and a pressure of 1.45 atm when the temperature is 310 K. What is the pressure when the volume is increased to 180 cm3 and the temperature is reduced to 280K?
0.62 atm

55. Combined Gas Law problems
2. Air is transferred from a 75 L tank where the pressure is 125 psi and the temperature is 288 K to a tire with a volume of 6.1 L and a pressure of 25 psi. What is the new temperature?
4.69 K

56. Combined Gas Law problems
3. A helium balloon at 28ºC has a volume of 1.8 L and a pressure of 102 kPa. What is the volume of the balloon when is rises into the atmosphere where the pressure is 85 kPa and the temperature is 4ºC?
1.99 L

57. Wrap it up with a video
(2:49)
If that doesn’t work:

58. Let’s practice Work on 1. Properties of Gases Questions
2. Mixed up Gas Law problems
For each problem – identify the gas law, predict if the unknown value will increase or decrease, and then solve.