1. Chapter 11: Gases Chem 1110 Figures: Basic Chemistry 3 rd Ed., Timberlake and Timberlake

2. Forces in Matter We know that matter is held together by a variety of forces: Electrons are attracted to protons Cations (+) are attracted to anions (-) Atoms in molecules are held together by bonds sharing electrons Bonds and molecules may have a net dipole moment which sets up positive and negative areas that are attracted to each other

3. Forces in Matter Intermolecular forces are attractive forces between molecules: 1.Weaker than bonds 2.Help to determine the state of matter: Solid, Liquid, or Gas Intermolecular forces which organize matter are opposed by the motion of molecules which disorganize matter

4. Kinetic Molecular Theory of Gases Five statements which explain the physical behavior of solids, liquids, and gases Primary Idea: particles are always in motion and contain two types of energy: Kinetic Energy: energy matter possesses due to particle motion: DISRUPTIVE! Potential Energy: stored energy in matter due to composition and structure: ORGANIZING!

5. Kinetic Molecular Theory of Gases: The Five Statements 1.Particles are in rapid straight line motion Possess kinetic energy 2.Assume NO attractive forces between gas particles 3.Particles are far apart 4.Particles have very small volumes compared to the volume of the container they occupy 5.Kinetic Energy increases with increasing temperature

6. Atmospheric Pressure Air in the atmosphere exerts a pressure: We have lived under this pressure always and do not recognize or “feel” it, but it is there At sea level, a column of air (1 in 2 ) = 14.7 lbs We say the pressure is 14.7 lbs/in 2 or psi At higher altitudes (Denver, Mt Everest) have a shorter column of air, therefore less weight Low altitudes (Death Valley) - more weight Scuba divers under 10 m water ≈ 14.7 psi

7. Atmospheric Pressure The air in the atmosphere exerts a pressure (force) on everything below it We have lived under this pressure always, but we do not recognize or “feel” it

8. Measuring Atmospheric Pressure We use a barometer to measure pressure Invented by Evangelista Torricelli in 1600s Pressure of atmosphere is compared to pressure of a mercury column

9. A.The downward pressure of the Hg in a barometer is _____ than (as) the pressure of the atmosphere: 1) greater 2) less 3) the same B.A water barometer is 13.6 times taller than a Hg barometer (D Hg = 13.6 g/mL) because: 1) H 2 O is less dense (less heavy) 2) H 2 O is heavier 3) Air is more dense than H 2 O Learning Check

10. Units of Pressure Pressure is the force acting on a specific area: Pressure (P) = force area

11. Measuring Atmospheric Pressure The height of a column of mercury may be measured in many units (Sea Level, 0 °C):  1 atmosphere  14.7 psi  760 mm Hg  760 torr  76.0 cm Hg  29.9 inches of Hg (weather stations) Each of these are conversion factors!!

12. How many atmospheres if the pressure is measured as 635 torr? in Hg? Learning Check

13. Ideal Gases 1.Gases are mostly space with a large separation between atoms 2.Atoms move rapidly in straight line motion, change direction on collision 3.No intermolecular attractive forces in a gas 4.Collisions do not change net energy of the gas but transfer energy 5.Individual particles move at different speeds

14. Real Gases Real gases approach IDEAL behavior when we ignore intermolecular forces: Low Pressure o Lots of space so can “ignore” each other. High Temperature o Moving quickly so whiz past each other

15. Properties of Gases Gases are described by Four Properties: Pressure (P) Volume (V) Temperature (T) Amount(n)

16. Gas Laws Gases are the most compressible state of matter as there is mostly space between particles Let’s look at how a sample of gas responds to changes in pressure and temperature: o Pressure o Temperature o Volume

17. Ideal Gas Law Relationships P and V are inversely related As pressure increases, volume decreases As pressure decreases, volume increases P is directly related to T As temperature increases, pressure increases As temperature decreases, pressure decreases V is also directly related to T As temperature increases, volume increases As temperature decreases, volume decreases

18. Ideal Gas Law PV = nRT P = pressure in atmospheres V = volume in liters T = temperature in Kelvin n = moles of gas R = gas constant = 0.0821 L∙atm mole∙K

19. How many moles of gas are present if a sample of some unknown gas at 2.00 atm and 0°C takes up 1.12 liters volume? Assuming we have 5.8 grams of the gas, what is its molecular weight? Learning Check

20. Boyle’s Law Boyle’s Law states: the pressure of a gas is inversely related to its volume (at constant T) if the pressure (P) increases, then the volume decreases

21. Boyle’s Law P 1 V 1 = P 2 V 2 Influenced by the work of Torricelli o Creating a vacuum over mercury (barometer) Discovered the “Spring of Air” o Gases behave elastically o Spring back to original volume after compressed

22. Boyle’s Law P 1 V 1 = P 2 V 2 At constant T, the volume of a fixed sample of gas (same n) varies inversely with the pressure exerted Double the pressure → one half the volume

23. Learning Check For a cylinder containing helium gas, indicate if cylinder A or cylinder B represents the new volume for the following changes (n and T are constant): 1) Pressure decreases 2) Pressure increases

24. Learning Check A sample of helium gas in a balloon has a volume of 6.4 L at a pressure of 0.70 atm. At 1.40 atm (T and n constant), is the new volume represented by A, B, or C?

25. P and V in Inhalation During inhalation: the lungs expand the volume of the lungs increases (↑V) pressure in the lungs decreases (↓P) air flows toward the lower pressure in the lungs

26. P and V in Exhalation During exhalation: the lungs contract the volume of the lungs decreases (↓V) pressure in the lungs increases (↑P) air flows from the higher pressure in the lungs

27. Charles’s Law Charles’s Law states: the temperature of a gas is directly related to the volume (at constant P) when the temperature of a gas increases, its volume increases (at constant P)

28. Charles’ Law V 1 V 2 T 1 T 2 Influenced by work with hot air balloons Discovered that hot air was less dense than cold air –Heating air in balloon will allow it to rise –Cooling the air will cause it to return to earth =

29. Charles’ Law At constant pressure (P), the volume of a fixed sample of gas (same n) is directly proportional to its Kelvin temperature Doubling the Kelvin temperature → doubles the volume of the gas V 1 V 2 T 1 T 2 =

30. Gay-Lussac’s Law: P and T Gay-Lussac’s Law states: the pressure exerted by a gas is directly related to the Kelvin temperature (at constant V) when the temperature of a gas increases, its pressure increases (at constant V)

31. Gay-Lussac’s Law Also based on work with hot air balloons At constant V, the pressure of a fixed sample of gas (same n) is directly proportional to its temperature Doubling the Kelvin temperature → doubles the pressure of the gas Also discovered that the composition of the atmosphere does not change with decreasing pressure (increasing altitude) P 1 P 2 T 1 T 2 =

32. Learning Check Use the gas laws to complete the following statements with increases or decreases: A.Pressure _______ when V decreases. B.When T decreases, V _______. C. Pressure _______ when V changes from 12 L to 4 L. D. Volume _______ when T changes from 15 °C to 45 °C.

33. Combined Gas Law Can be derived directly from the Ideal Gas Law: PV = nRT P 1 V 1 P 2 V 2 T 1 T 2 =

34. A small cylinder of nitrogen gas (5.7 L) is under 5.03 atm of pressure. What would be the volume at a pressure of 754 torr? Learning Check

35. A helium balloon has a volume of 2.5 L at 25 °C. What is the volume of the balloon in liquid nitrogen at -196 °C? Learning Check

36. A rubber glove is filled with carbon dioxide gas at a volume of 1.73 L, 23 °C and 743 torr. What will the temperature of the gas be (in °C) if the pressure is increased to 1.71 atm and the volume is allowed to increase to 2.00 L? Learning Check

37. Why do empty spray paint cans at 1.05 atm and 25 °C explode when put in a bonfire at 451°C? Take Home

38. Avogadro's Law: V and n Avogadro’s Law states: the volume of a gas is directly related to the number of moles (n) of gas equal volumes of any gas at the same temperature and pressure have the same number of molecule

39. Molar Volume and STP Chemists have defined a specific set of conditions known as standard temperature and pressure (STP) as: 1 atmosphere and 0 °C Under these conditions (STP), 1 mole of any gas will occupy exactly 22.4 L Consequently, Molar volume is defined as: 1 mole of gas = 22.4 L at STP

40. Molar Volume What is the volume occupied by 2.75 mole of N 2 gas at STP?

41. What is the density of SO 2 gas at STP? Learning Check

42. Gases in Chemical Equations The volume (or amount) of a gas in a chemical reaction can be calculated from: The ideal gas law Mole-mole factors from the balanced equation The molar mass

43. Using the Ideal Gas Law Within a Chemical Equation What volume (in L) of Cl 2 gas at 1.20 atm and 27 °C is needed to completely react with 1.50 g of aluminum? 2 Al(s) + 3 Cl 2 (g) 2 AlCl 3 (s)

44. What volume (L) of O 2 at 24 °C and 0.950 atm is needed to react with 28.0 g of NH 3 ? 4 NH 3 (g) + 5 O 2 (g) 4 NO(g) + 6 H 2 O(g) Learning Check

45. What mass of Fe will react with 5.50 L of O 2 at STP? 4 Fe(s) + 3 O 2 (g) 2 Fe 2 O 3 (s) Take Home

46. Mixed Samples of Gases Some gas samples are made up of more than one type of gas: Air is a good example and includes:  N 2, O 2, CO 2, H 2 O, Ar, traces of others If we have a homogeneous mixture of gases, we can determine the individual contributions of pressures from each gas to the total… Dalton’s Law of Partial Pressures

48. Law of Partial Pressures P Total = Σ P each gas or P Total = P gas1 + P gas2 + P gas3 P Air = P N 2 + P O 2 + P CO 2 + …

49. Law of Partial Pressures Understanding partial pressures of gases is very important for medical applications: High P O 2 can harm body tissues yet low P O 2 leads to other issues Dissolved nitrogen in the blood from deep water or extended scuba diving leads to decompression sickness or the bends o Pressurized air is primarily N 2 and O 2

50. The Gases We Breathe The air we breathe: is a mixture of gases contains mostly N 2 and O 2 as well as small amounts of other gases

51. 51 Gas Exchange During Breathing

52. Blood Gases In the lungs, O 2 enters the blood, while CO 2 from the blood is released In the tissues, O 2 enters the cells, while CO 2 is released into the blood

53. Blood Gases In the body: O 2 flows into the tissues because the partial pressure of O 2 is higher in the blood and lower in the tissues CO 2 flows out of the tissues because the partial pressure of CO 2 is higher in the tissues and lower in the blood

54. Scuba Diving When a scuba diver is below the ocean surface, the increased pressure causes more N 2 (g) to dissolve in the blood If a diver rises too fast, the dissolved N 2 can form bubbles in the blood, a dangerous and painful condition called "the bends” For deep descents, helium, which does not dissolve in the blood, is added to O 2 Under water, the pressure on a diver is greater than the atmospheric pressure

55. Hyperbaric Chamber

56. Forces in Matter So far we have focused on gases, specifically Ideal Gases Let’s revisit liquids and solids: We can no longer assume no attractions between particles that are close together! We must re-examine intermolecular forces!

57. Forces in Matter Revisited Intermolecular forces are attractive forces between molecules: 1.Weaker than bonds 2.Help to determine the state of matter: Solid, Liquid, or Gas Intermolecular forces which organize matter are opposed by the motion of molecules which disorganize matter

58. Boiling and Vapor Pressure Boiling Point: a liquid boils when its vapor pressure equals atmospheric pressure Vapor Pressure: the pressure exerted by a vapor above a liquid when the liquid and vapor are in an equilibrium state Water at sea level: Boiling Point = 100 °C o Under column of air at 1 atm, 760 mm Hg, 14.7 psi, 760 torr…

59. Vapor Pressure of Water changes based on Altitude (Pressure)

60. Boiling Point of Water changes based on Altitude (Pressure)

61. Learning Check In each of the following pairs of atmospheric and vapor pressure, indicate if water will or will not boil: Atmospheric Vapor Boiling Pressure Pressure Occurs? A. 760 mmHg 760 mmHg B. 960 mmHg 760 mmHg C. 520 mmHg 620 mmHg

62. Evaporation Liquids evaporate when individual molecules reach “escape velocity” to the gas phase: o Reach their boiling point. o Agrees with KMT – various speeds of particles Some liquids evaporate more easily than others –Have a high vapor pressure – close to 1 atm Volatile liquids readily evaporate at room temperature and have high vapor pressures

63. Evaporation