1. “He could clear the savanna after every meal
“He could clear the savanna after every meal!” UNIT 10: Gases & Phase Changes

2. Outline of a Gassy Unit 10.1 Properties of Gases
10.2 Temperature and Pressure
10.3 Combined Gas Law
10.4 Ideal Gas Law
10.5 Phase Change Diagrams

3. 10.1 Learning Target I can describe the properties of gases. Shape
Volume
Density
Fluidity
Diffusion/Effusion

4. 10.1 – Properties of Gases Shape: indefinite Volume: indefinite
Compressible (decrease)
Expandable (increase)
Tennis ball
Marshmallow…
Volume: indefinite
Indefinite shape – the room air pockets.
Fire syringe… cotton ball for compressible.

5. 10.1 – Properties of Gases Density – gases have a low density
Small amount of mass in a given space.
What would happen if the volume was compressed?
Balloon demo…

6. 10.1 – Properties of Gases Gases are fluid! Color Pouring CO2
Many are colorless.
Oxygen, nitrogen, and water.
Gases with color are poisonous.
Iodine

7. 10.1 – Properties of Gases Diffusion Effusion Definition:
Molecules of different gases mix easily and spread throughout a container.
Gas particles spontaneously pass through a small opening.
Example:
Ex: Bacon in the morning… or pizza…
Ex. Helium balloons

8. 10.2 Learning Target
Describe pressure and temperature in terms of kinetic molecular theory.
Convert between different units of temperature and convert between different units of pressure.

9. 10.2 – Temperature and Pressure
Ideal Gas
“Perfect” gas
Assumes the following:
1. Gas molecules have no volume.
2. Gas molecules move in straight lines until they collide.
3. Gas molecules are neither attracted nor repelled by one another.

10. 10.2 – Kinetic molecular theory
Gas molecules are constantly in motion and collide with each other and with the walls of a container
Particles move faster with increased temps
Gases are made of mostly empty space and just a few fast moving particles

11. 10.2 – Variables of a Gas (P) Pressure (V) Volume (T) Temperature
(n) Amount of gas in moles

12. 10.2 – Variables of a Gas
A variable is a factor that is likely to change.
Pressure, temperature, and volume of a gas are likely to change.
Pressure, volume, and temperature are interdependent.
When one variable changes, they all do.

13. 10.2 – Pressure
Measures: Force exerted by moving gas particles and by collisions with their container.

14. 10.2 – Pressure Units: atm (atmosphere)
- 1 atm of pressure is the average pressure at sea level
Important Conversions:
1 atm = 760 mmHg (millimeters of Mercury)
= 760 torr
= kPa (kilo Pascals)
= 14.7 psi (pounds per square inch)

15. 10.2 – volume Measures: amount of space that a gas occupies
Units: Liters (L)
Important Conversions: 1 L = 1000 mL

16. 10.2 – Temperature Measures: average kinetic energy of gas particles.
Units: Kelvin (K)
The Celsius scale is NOT used for gases because gases can still have kinetic energy at negative and 0o C.

17. 10.2 – Temperature Kelvin Scale and Absolute Zero
Absolute Zero = 0 Kelvin represents the temperature at which a gas has NO kinetic energy
Atoms at Absolute Zero

18. oC + 273 = K K – 273 = oC 10.2 – Temperature Converting Temperature
Important Conversions:
oC = K
K – 273 = oC

19. 10.2 – Standard Temperature and Pressure
STP = Standard Temperature and Pressure
Exactly 0oC and 1 atm
At STP, one mole of gas (6.02 x1023 particles)
occupies 22.4 L
If a gas is not held at STP, then volume is recalculated

20. 10.3 – Learning Targets I can use the combined gas laws!
You will be studying the four variables that effect the behavior of gases.
Pressure
Temperature
Volume
Number of moles of gas particles

21. 10.3 – Combined Gas Law
Relates pressure, temperature, volume, and moles of a gas
Relates initial and final conditions
Variables that do not change are constants and are not included in the equation

22. 10.3 – Combined Gas Laws
The left side (1) represents the initial conditions of the gas
The right side (2) represents the final conditions of the gas

23. 10.3 – Charles’ law What changes? And How? What stays the same?
Volume increases, temperature increases
What stays the same?
Pressure and moles are held constant (toss ‘em)

24. 10.3 – Charles’ law Equation
Remember: Temperatures must be in Kelvin

25. 10.3 – Charles’ law Demo

26. 10.3 – Charles’ law Graph
Direct Relationship: both variables increase together

27. 10.3 – Charles’ law Example
A gas sample at 25 °C and 752 mL is heated to 50 °C , what is the new volume?

28. 10.3 – Gay – Lussac’s Law What changes? And how?
As temperature of a gas increases, the pressure also increases
What stays the same?
Volume and moles are held constant (toss ‘em)

29. 10.3 – Gay- Lussac’s Equation
Pressure units on both sides of the equation must be the same
Temperature must be in Kelvin

30. 10.3 – Gay- Lussac’s Demo

31. 10.3 – Gay- Lussac’s Graph
Direct Relationship: Both variables increase together

32. 10.3 – Gay- Lussac’s Example
Q: A gas has a pressure of atm at 50.0 °C. What is the pressure at standard temperature?

33. 10.3 – Boyle’s Law What changes? And How?
When Pressure increases, Volume decreases
What stays the same?
Temperature and moles are held constant (toss ‘em)

34. 10.3 – Boyle’s Law Equation P1V1 = P2V2
Remember: Pressure units on both sides of the equation must be the same

35. 10.3 – Boyle’s Law Demo

36. 10.3 – Boyle’s Law Graph
Inverse Relationship: an increase in one variable with a simultaneous decrease in the other

37. 10.3 – Boyle’s Law Example
Q: A 1.0 L sample of gas is held at standard pressure, 1.0 atm. The pressure of the gas is reset to 152 mmHg. What is the new volume of the gas?

38. 10.3 – Avogadro’s Law
Avogadro stated that as the number of moles of a gas increases, volume increases.

39. 10.3 – Avogadro’s Law
The temperature and pressure are kept constant.

40. 10.3 – Avogadro’s Law “Demo”

41. Chemistry Valentines You are like Fluorine, Iodine, and Neon…
You are FINe!
Are you made of copper and tellurium?
Because you are CuTe!

42. 10.3 – Mini Quiz Review P1V1 = P2V2
A container of gas has a volume of 10 L at a pressure of 1.0 atm. What would be the new volume of the gas if the pressure was increased to 2.0 atm?

43. 10.3 – Mini Quiz Review P1V1 = P2V2
A gas sample at 40.0 °C occupies a volume of 2.32 L. If the temp is raised to 75.0 °C, what will the volume be?

44. 10.3 – Mini Quiz Review P1V1 = P2V2
The pressure of a gas in a tank is 3.2 atm at 22 °C. If the temp rises to 60.0 °C, what will be the gas pressure in the tank?

45. 10.3 – Mini Quiz Review P1V1 = P2V2
The number of moles in a balloon changed from 4.01 to If the volume of the balloon was originally 1.13 L, what is the new volume?

46. 10.3 – The master Equation
The gas left in a used aerosol can is at the pressure of kPa at 27 °C. If the can is thrown into the fire, what will the internal pressure of the gas be when its temperature reaches 927 °C?

47. 10.3 – The master Equation
A gas at 110 kPa and 30.0 °C fills a flexible container with an initial volume of 2.00 L. If the temperature is raised to °C and the pressure increased to 440 kPa, what is the new volume?

48. Review!
When a sample of gas is under lower pressure, with no temperature change, what will happen to…
The volume of a gas?

49. Review!
If air is trapped in a syringe at a constant temperature, but more pressure is applied, what will happen to the volume?

50. Review!
What happens to a balloon filled with a light gas outside in the freezing cold?
The balloon’s volume?

51. 10.4 Learning Targets
Use the ideal gas law.

52. 10.4 – Ideal Gas PV = nRT P = pressure (units can vary)
V = volume (Liters)
n = moles
T = temperature (K)
R is the Ideal Gas Constant
Use if conditions (P, V, n, or T) DO NOT change

53. 10.4 – Ideal Gas
Values of R: (with units)
Atm
kPa
mm Hg or torr

54. 10.4 – Ideal Gas Example 1
A sample of O2 gas collected at 30°C has a volume of 0.25 L and a pressure of 1.3 atm. How many moles of oxygen are present?

55. 10.4 – Ideal Gas Example 2
A sample of He gas contains 0.5 moles. At STP, what is the volume of the gas?