1. CHEMISTRY CHAPTER 11
TEMPERATURE
A measure of the average kinetic energy of the particles of a sample. It is the property of matter that determines if heat can be transferred from one body to another, and the direction of that transfer.

2. COMMON TEMPERATURE SCALES
English
(Fahrenheit)
Metric
(Celsius)
S.I.
(Kelvin)
abbreviation F C K
water boils
212°
100°
373
human body temp.
~98.6°
37°
310
water freezes
32° 0°
273
absolute zero
-460°
-273°

3. Absolute zero: all motion stops A kelvin (K) is the S. I
Absolute zero: all motion stops A kelvin (K) is the S.I. unit of temperature. Kelvin temperatures are written without the degree symbol (°). A temperature difference of 1 kelvin is a 1 degree difference on the Celsius scale.

4. CONVERSION FACTORS

5. EXAMPLES
1. 10° C to K: K = °C = 10° = K to °C °C = K – = 380 – = , round to 107° C

6. Section 1 Gases and Pressure
Chapter 11. GASES
Section 1 Gases and Pressure
Pressure and Force
Pressure (P) is defined as the force per unit area on a surface.
Gas pressure is caused by collisions of the gas molecules with each other and with surfaces with which they come into contact.

7. The SI unit of force is the newton (N).
Measuring Pressure
The SI unit of force is the newton (N).
The SI unit of pressure is the pascal (Pa) = 1 N/m2
Because a pascal is so small, we usually use kilopascals (kPa).

8. Other units:
The height of a column of mercury: 1 mm Hg = 1 torr
Standard atmospheric pressure at sea level and 0° C:
1 atmosphere (atm) = 760 torr = kPa (atmospheric pressure varies, but 1 atm is defined to be exactly 760 torr)

9. Evangelist Torricelli
Blaise Pascal
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Evangelist Torricelli
en.wikinoticia.com

10. Pounds per square inch (psi):
1 atm = 14.7 psi
1 psi = 6.89 kPa
Atmospheric pressure is measured with a barometer.

11. Barometer

12. Dalton’s Law of Partial Pressures
The pressure of each gas in a mixture is called the partial pressure of that gas.
John Dalton, the English chemist who proposed the atomic theory, discovered that the pressure exerted by each gas in a mixture is independent of that exerted by other gases present.

13. Dalton’s law of partial pressures states that the total pressure of a gas mixture is the sum of the partial pressures of the component gases.

14. Dalton’s Law of Partial Pressures

15. Equation for Dalton’s Law of Partial Pressures

16. Gases Collected by Water Displacement
Gases produced in the laboratory are often collected over water. The gas produced by the reaction displaces the water in the reaction bottle.
Dalton’s law of partial pressures can be applied to calculate the pressures of gases collected in this way.

17. Water molecules at the liquid surface evaporate and mix with the gas molecules. Water vapor, like other gases, exerts a pressure known as vapor pressure.
To determine the pressure of a gas inside a collection bottle, you would use the following equation, which is an instance of Dalton’s law of partial pressures.
Patm = Pgas +

18. If you raise the bottle until the water levels inside and outside the bottle are the same, the total pressure outside and inside the bottle will be the same.
Reading the atmospheric pressure from a barometer and looking up the value of at the temperature of the experiment in a table, you can calculate Pgas.

19. Particle Model for a Gas Collected Over Water

20. Sample Problem
Oxygen gas from the decomposition of potassium chlorate, KClO3, was collected by water displacement. The barometric pressure and the temperature during the experiment were torr and 20.0°C. respectively. What was the partial pressure of the oxygen collected?

21. Solution
Given: PT = Patm = torr
= 17.5 torr (vapor pressure of water at 20.0°C, from table A-8 in your book)
Patm =
Unknown: in torr
Solution:
start with the equation:
rearrange algebraically to:

22. substitute the given values of Patm and into the equation:

23. Section 2. The Gas Laws
Boyle’s Law: Pressure-Volume Relationship
Robert Boyle discovered that doubling the pressure on a sample of gas at constant temperature reduces its volume by one-half.

24. This is explained by the kinetic-molecular theory:
The pressure of a gas is caused by moving molecules hitting the container walls.
If the volume of a gas is decreased, more collisions will occur, and the pressure will increase.
If the volume of a gas is increased, less collisions will occur, and the pressure will decrease.

25. Boyle’s Law states that if temperature is constant, the volume of a gas is inversely proportional to pressure.

26. Boyle’s law can be expressed as:
PV = k or V=k/P
P is the pressure, V is the volume, and k is a constant.
If there is a change from condition 1 to condition 2 (and temperature remains constant), then:
P1V1 = P2V2

27. Example (p. 370): A sample of oxygen gas has a volume of 150
Example (p. 370): A sample of oxygen gas has a volume of mL when its pressure is atm.
What will the volume of the gas be at a pressure of atm if the temperature remains constant?

28. Given:V1 of O2 =
P1 of O2 =
P2 of O2 =
Unknown:
Solution: Rearrange the equation for Boyle’s law
(P1V1 = P2V2) to obtain V2.

29. Given:V1 of O2 = mL
P1 of O2 = atm
P2 of O2 = atm
Unknown: V2 of O2 in mL
Solution: Rearrange the equation for Boyle’s law
(P1V1 = P2V2) to obtain V2.

30. Check: pressure went up, volume went down.
Substitute the given values of P1, V1, and P2 into the equation to obtainV2:
Check: pressure went up, volume went down.

31. If pressure is constant, gases expand when heated.
Charles’s Law: Volume-Temperature Relationship
If pressure is constant, gases expand when heated.
When the temperature increases, the volume of a fixed number of gas molecules must increase if the pressure is to stay constant.

32. At the higher temperature, the gas molecules move faster
At the higher temperature, the gas molecules move faster. They collide with the walls of the container more frequently and with more force.
The volume of a flexible container must then increase in order for the pressure to remain the same.

33. Charles’s Law

34. In 1787 Charles discovered that all gases expand by about 1/273 for an increase in temperature of 1° C near 0° C. Extrapolating backwards from measurements at several temperatures gives a volume of 0 at
What is this temperature?

35. In 1787 Charles discovered that all gases expand by about 1/273 for an increase in temperature of 1° C near 0° C. Extrapolating backwards from measurements at several temperatures gives a volume of 0 at
What is this temperature?
Absolute zero

36. wps.prenhall.com

37. Charles’s law states that the volume of a fixed mass of gas at constant pressure is proportional to the Kelvin temperature.

38. Charles’s law can be expressed as:
V is the volume, T is the Kelvin temperature, and k is a constant.
For a change from condition 1 to condition 2:

39. Ex. (p. 372): A gas sample has a volume of 752 mL at 25° C
Ex. (p. 372): A gas sample has a volume of 752 mL at 25° C. What will be the volume at 50° C if the pressure remains constant?
Need to change to Kelvin temperatures: (K = °C + 273)
T1 = = 298 K
T2 = = 323 K

40. Check: T increased, V increased.

41. Gay-Lussac’s Law: Pressure-Temperature Relationship
With increasing temperature, kinetic energy of gas particles increases, and they will exert more force on the sides of a container.
In 1802 Gay-Lussac found that the pressure increases by about 1/273 for an increase in temperature of 1° C at about 0°. Extrapolating backward gives a pressure of 0 at -273° C.

42. blog.cencophysics.com

43. Gay-Lussac’s law: the pressure of a fixed mass of gas at constant volume varies directly with the Kelvin temperature.

44. Gay-Lussac’s law can be expressed as:
P is the pressure, T is the Kelvin temperature, and k is a constant.
For a change from condition 1 to condition 2:

45. Example (p. 373): The gas in a container is at a pressure of 3
Example (p. 373): The gas in a container is at a pressure of 3.00 atm at 25°C. Directions on the container warn the user not to keep it in a place where the temperature exceeds 52°C. What would the gas pressure in the container be at 52°C?

46. Given: P1 = 3.00 atm
T1 = 25°C = 298 K
T2 = 52°C = 325 K
Unknown: P2 in atm

47. Check: T increased, P increased.

48. Summary of the Basic Gas Laws

49. Robert Boyle Jacques Charles Joseph Gay-Lussac crystalinks.com
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Joseph Gay-Lussac
chemistryland.com

50. The Combined Gas Law
Boyle’s law, Charles’s law, and Gay-Lussac’s law can be combined into a single equation that can be used for situations in which temperature, pressure, and volume all vary at the same time.

51. For a fixed amount of gas (grams or moles):
For a change from situation 1 to situation 2 (temperatures in Kelvin):

52. The other three laws can be obtained from the combined gas law by keeping T, P, or V constant:

54. Example (when P, V, and T all change) (p
Example (when P, V, and T all change) (p. 375): A helium-filled balloon has a volume of 50.0 L at 25°C and 1.08 atm. What volume will it have at atm and 10.0°C?

55. Given: V1 = 50.0 L
T1 = 25°C = 298 K T2 = 10°C = 283 K
P1 = 1.08 atm
P2 = atm
Unknown: V2 in L

56. Rearrange the equation for the combined gas law to obtain V2.

57. Section 3 Gas Volumes and the Ideal Gas Law
Measuring and Comparing the Volumes of Reacting Gases
Gay-Lussac discovered that in a reaction involving gases as reactants and products, the volumes were ratios of small whole numbers.
For example:
hydrogen gas + oxygen gas → water vapor (2 volumes) (1 volume) (2 volumes)

58. Avogadro’s Law
Avogadro explained this: equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

59. Avogadro’s Law
Amedeo Avogadro brittanica.com

60. So the ratios of volumes in a reaction are the same as the ratios of molecules or the ratios of moles:
2 mol H2 + 1 mol O2 → 2 mol H2O
2H O → H2O
These ideas lead to the conclusion that the volume of a gas is proportional to the number of moles (n): V = kn

61. Ex. – what is the volume of 3 mol N2 at STP?
Molar Volume of a Gas
At standard temperature and pressure (STP) (0° C and 1 atm), 1 mole of a gas has a volume of 22.4 L.
Ex. – what is the volume of 3 mol N2 at STP?
3 mol x (22.4 L/1 mol) = 67.2 L

62. Example 2: how many moles are in 5.00 L of a gas?

63. The Ideal Gas Law is the relationship among pressure, volume, temperature, and number of moles of a gas.
PV = nRT
where n = number of moles
T = Kelvin temperature
R = gas constant

64. Equation for the Ideal Gas Law - 75208

65. The Ideal Gas Constant (R) is expressed in different units depending on the units of pressure and volume.

66. Ideal Gas Law

67. Example: What is the pressure in atmospheres exerted by a 0
Example: What is the pressure in atmospheres exerted by a mol sample of nitrogen gas in a 10.0 L container at 298 K?
Given: V = 10.0 L n = mol
T = 298 K
Unknown: P in atm

68. Solution: Use the ideal gas law, which can be rearranged to find the pressure, as follows.
Since we want P in atm, the value of (L•atm)/(mol•K) is used for R.