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I. Physical Properties. Real vs. Ideal Gases: b Ideal gas = an imaginary gas that conforms perfectly to all the assumptions of the kinetic-molecular theory.

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Presentation on theme: "I. Physical Properties. Real vs. Ideal Gases: b Ideal gas = an imaginary gas that conforms perfectly to all the assumptions of the kinetic-molecular theory."— Presentation transcript:

1 I. Physical Properties

2 Real vs. Ideal Gases: b Ideal gas = an imaginary gas that conforms perfectly to all the assumptions of the kinetic-molecular theory We will assume that the gases used for the gas law problems are ideal gases.

3 Real Gases vs. Ideal Gases: b Real gas = a gas that does not behave completely according to the assumptions of the kinetic- molecular theory. b All real gases deviate to some degree from ideal gas behavior. However, most real gases behave nearly ideally when their particles are sufficiently far apart and have sufficiently high kinetic energy.

4 Causes of non-ideal behavior: The kinetic-molecular theory is more likely to hold true for gases whose particles have NO attraction for each other.

5 Causes of non-ideal behavior: 1. High pressure (low volume): Space taken up by gas particles becomes significant Intermolecular forces are more significant between gas particles that are closer together

6 Causes of non-ideal behavior: 2. Low temperature: Gas particles move slower so intermolecular forces become more important

7 b Kinetic Molecular Theory (KMT) = the idea that particles of matter are always in motion and that this motion has consequences. b theory developed in the late 19 th century to account for the behavior of the atoms and molecules that make up matter KMT (Kinetic Molecular Theory)

8 based on the idea that particles in all forms of matter are always in motion and that this motion has consequences KMT (Kinetic Molecular Theory) SOLID LIQUID GAS

9 can be used to explain the properties of solids, liquids, and gases in terms of the energy of particles and the forces that act between them KMT (Kinetic Molecular Theory)

10 B. Kinetic Molecular Theory – Ideal gas b KMT describing particles in an IDEAL gas: have no volume. have elastic collisions. are in constant, random motion. dont attract or repel each other. have an avg. KE directly related to Kelvin temperature.

11 C. Kinetic Molecular Theory - Real Gases b KMT describing particles in a REAL gas: have their own volume attract each other b Gas behavior is most ideal… at low pressures at high temperatures in nonpolar atoms/molecules

12 D. Characteristics of Gases- using KMT b Gases expand to fill any container. b KMT - gas particles move rapidly in all directions without significant attraction or repulsion between particles

13 D. Characteristics of Gases- using KMT b Gases are fluids (like liquids). KMT - No significant attraction or repulsion between gas particles; glide past each other

14 D. Characteristics of Gases- using KMT b Gases have very low densities. KMT - particles are so much farther apart in the gas state sodium in the solid state: sodium in the liquid state: sodium in the gas state:

15 b Gases can be compressed. KMT - gas particles are far apart from one anther with room to be squished together D. Characteristics of Gases- using KMT

16 b Gases undergo diffusion & effusion. KMT – gas particles move in continuous, rapid, random motion D. Characteristics of Gases- using KMT Effusion

17 E. Temperature ºF ºC K K = ºC b Always use Kelvin temperature when working with gases.

18 F. Pressure Which shoes create the most pressure?

19 F. Pressure b Why do gases exert pressure? Gas particles exert a pressure on any surface with which they collide! More collisions = increase in pressure!

20 F. Pressure b Barometer = measures atmospheric pressure b The height of the Hg in the tube depends on the pressure The pressure of the atmosphere is proportional to the height of the Hg column, so the height of the Hg can be used to measure atmospheric pressure! Mercury Barometer

21 F. Pressure b Pressure UNITS kPa (kilopascal) 1 atm 760 mm Hg 760 torr

22 G. STP Standard Temperature & Pressure 0°C (exact)1 atm (exact) 273 K101.3 kPa 760 mm Hg (exact) 760 torr (exact) STP

23 II. The Gas Laws Gases

24

25 A. Boyles Law P V PV = k

26 A. Boyles Law b The pressure and volume of a gas are INVERSELY related at constant mass & temp P V

27 A. Boyles Law Real life application: When you breathe, your diaphragm moves downward, increasing the volume of the lungs. This causes the pressure inside the lungs to be less than the outside pressure so air rushes in.

28 A. Boyles Law Ex: Halving the volume leads to twice the rate of collisions and a doubling of the pressure.

29 A. Boyles Law As the volume increases, the pressure decreases!

30 V T B. Charles Law

31 V T b The volume and temperature (K) of a gas are DIRECTLY related at constant mass & pressure

32 B. Charles Law b Real life application: Bread dough rises because yeast produces carbon dioxide. When placed in the oven, the heat causes the gas to expand, and the bread rises even further.

33 B. Charles Law b As temperature decreases, the volume of the gas decreases Liquid nitrogens temp. is about 63K or -210 ºC or -346 ºF!

34 B. Charles Law b As temperature decreases, the volume of the gas decreases

35 B. Charles Law b NUMBER OF PARTICLES & PRESSURE ARE CONSTANT!!!

36 P T C. Guy-Lussacs Law

37 P T b The pressure and temperature (K) of a gas are DIRECTLY RELATED at constant mass & volume

38 C. Guy-Lussacs Law b When the temp. of a gas increases (KE increases) and gas particles move faster and hit container walls more frequently and collisions are more forceful

39 C. Guy-Lussacs Law b Real life application: The air pressure inside a tire increases on a hot summer day.

40 = k Boyles PV P Guy Lussacs T V Charles T PV T D. Combined Gas Law P1V1T1P1V1T1 = P2V2T2P2V2T2

41 E. EXAMPLE Problems b You need your calculators!

42 C. Johannesson GIVEN: V 1 = 473 cm 3 T 1 = 36°C = 309K V 2 = ? T 2 = 94°C = 367K WORK: Gas Law Problems 1.) A gas occupies 473 cm 3 at 36°C. Find its volume at 94°C. T V V 2 = (473 cm 3 )(367 K) (309 K) V 2 = 562 cm 3

43 C. Johannesson GIVEN: V 1 = 100. mL P 1 = 150. kPa V 2 = ? P 2 = 200. kPa WORK: V 2 = P 1 V 1 P 2 Gas Law Problems 2.) A gas occupies 100. mL at 150. kPa. Find its volume at 200. kPa. BOYLES LAW P 1 V 1 = P 2 V 2 P V V 2 = (150.kPa)(100.mL) 200.kPa V 2 = 75.0 mL

44 C. Johannesson GIVEN: V 1 = 7.84 cm 3 P 1 = 71.8 kPa T 1 = 25°C = 298 K V2 = ?V2 = ? P 2 = kPa T 2 = 273 K WORK: V 2 = P 1 V 1 T 2 P 2 T 1 V 2 = (71.8 kPa)(7.84 cm 3 )(273 K) (101.3 kPa) (298 K) V 2 = 5.09 cm 3 Gas Law Problems 3.) A gas occupies 7.84 cm 3 at 71.8 kPa & 25°C. Find its volume at STP. P T V

45 C. Johannesson GIVEN: P 1 = 765 torr T 1 = 23°C = 296K P 2 = 560. torr T 2 = ? WORK: T 2 = P 2 T 1 P 1 Gas Law Problems 4.) A gas pressure is 765 torr at 23°C. At what temperature will the pressure be 560. torr? P T T 2 = (560. torr)(296K) 765 torr T 2 = 217 K

46 III. Standard Molar Volume, Gas Densities & Molar Mass Gases

47 A. Standard Molar Volume b The volume occupied by one mole of a gas at STP L/mol or about 22.4 L/mol b In other words, one mole of any ideal gas at STP will occupy 22.4 L

48 B. Example Problems-standard molar volume 1.) A chemical reaction is expected to produce mol of oxygen gas. What volume of gas in L will be occupied by this gas sample at STP? mol O L O 2 1 mol O 2 = 1.52 L O 2

49 B. Example Problems-standard molar volume 1.) A chemical reaction is expected to produce mol of oxygen gas. What volume of gas in L will be occupied by this gas sample at STP? mol O L O 2 1 mol O 2 = 1.52 L O 2

50 B. Example Problems-standard molar volume 2.) A chemical reaction produced 98.0 mL of SO 2 at STP. What mass (in grams) of the gas was produced? 98.0 mL SO 2 1 L SO 2 1 mol O 2 = g SO L SO mL SO 2 1 mol SO g SO 2

51 C. Density b The ratio of an objects mass to its volume. b D = M V b The volume (and density) of a gas will change when pressure and temperature change. Densities are usually given in g/L at STP

52 C. Density b For an ideal gas: Density (at STP) = molar mass standard molar volume

53 D. Example Problems- density 1.) What is the density of CO 2 in g/L at STP? g CO 2 1 mol CO 2 1 mol CO L CO 2 = 1.96 g/L CO 2

54 D. Example Problems- density 2.) What is the molar mass of a gas whose density at STP is 2.08 g/L g 22.4 L 1 L 1 mol = 46.6 g/mol

55 IV. More Gas Laws: Ideal Gas Law & Avogadro's Law Gases

56 V n A. Avogadros Law b Equal volumes of gases contain equal numbers of moles at constant temp & pressure

57 PV T VnVn PV nT B. Ideal Gas Law = k UNIVERSAL GAS CONSTANT R= L atm/mol K R=8.315 dm 3 kPa/mol K = R You dont need to memorize these values! Boyles, Charles, and Avogadros laws are contained within the ideal gas law! Merge the Combined Gas Law with Avogadros Law:

58 B. Ideal Gas Law GAS CONSTANT R= L atm/mol K R=8.315 dm 3 kPa/mol K PV=nRT You dont need to memorize these values! P= pressure V = volume n = moles T = temperature (in K) R = the ideal gas constant

59 C. Johannesson GIVEN: P = ? atm n = mol T = 16°C = 289 K V = 3.25 L R = L atm/mol K WORK: P = nRT V P =(0.412 mol)( L atm/mol K) (289K) 3.25L P = 3.01 atm C. Ideal Gas Law Problems 1.) Calculate the pressure in atmospheres of mol of He at 16°C & occupying 3.25 L. PV = nRT

60 C. Johannesson GIVEN: V = ? n = 85 g T = 25°C = 298 K P = kPa R = dm 3 kPa/mol K C. Ideal Gas Law Problems 2.) Find the volume of 85 g of O 2 at 25°C and kPa. PV = nRT = 2.7 mol WORK: 85 g O 2 1 mol O 2 = 2.7 mol g O 2 O 2 V = nRT P V =(2.7 mol)(8.315 dm 3 kPa/mol K) (298K) kPa V = 64 dm 3

61 C. Johannesson GIVEN: V = 1.00 L n = ? T = 28°C = 301 K P = 98.7 kPa R = L kPa/mol K C. Ideal Gas Law Problems 3.) At 28 C and 98.7 kPa, 1.00 L of an unidentified gas has a mass of 5.16 g. Calculate the number of moles of gas present and the molar mass of the gas. PV = nRT WORK: n = PV RT (98.7 kPa) (1.00L) (8.314 L kPa/mol K) (301 K) n = mol m = 5.16g mol = = 131 g/mol

62 Gases IV. Two More Laws: Daltons Law & Grahams Law

63 A. Daltons Law b The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases. P total = P 1 + P 2 + P 3...

64 A. Daltons Law P total = P 1 + P 2 + P 3...

65 A. Daltons Law When a H 2 gas is collected by water displacement, the gas in the collection bottle is actually a mixture of H 2 AND water vapor.

66 C. Johannesson GIVEN: P H2 = ? P total = 94.4 kPa P H2O = 2.72 kPa WORK: P total = P H2 + P H2O 94.4 kPa = P H kPa P H2 = 91.7 kPa A. Daltons Law 1.) Hydrogen gas is collected over water at 22.5°C. Find the pressure of the dry gas if the atmospheric pressure is 94.4 kPa. Look up water-vapor pressure on gas formula sheet for 22.5°C. Sig Figs: Round to least number of decimal places. The total pressure in the collection bottle is equal to atmospheric pressure and is a mixture of H 2 and water vapor.

67 C. Johannesson GIVEN: P gas = ? P total = torr P H2O = 42.2 torr WORK: P total = P gas + P H2O torr = P H torr P gas = torr 2.) A gas is collected over water at a temp of 35.0°C when the barometric pressure is torr. What is the partial pressure of the dry gas? Look up water-vapor pressure on gas formula sheet for 35.0°C. Sig Figs: Round to least number of decimal places. A. Daltons Law The total pressure in the collection bottle is equal to barometric pressure and is a mixture of the gas and water vapor.

68 B. Grahams Law b Diffusion = Spreading of gas molecules throughout a container until evenly distributed. b Effusion = Passing of gas molecules through a tiny opening in a container

69 B. Grahams Law KE = ½mv 2 b Speed of diffusion/effusion Kinetic energy is determined by the temperature of the gas. At the same temp & KE, heavier molecules move more slowly. Larger m smaller v

70 B. Grahams Law b KE = kinetic energy b m= molar mass b v = velocity KE = ½mv 2

71 C. Johannesson B. Grahams Law b Grahams Law b Grahams Law = Rate of effusion of a gas is inversely related to the square root of its molar mass. The equation shows the ratio of Gas As speed to Gas Bs speed.

72 1.) Determine the relative rate of effusion for krypton and bromine. Kr effuses times faster than Br 2. C. Grahams Law Problems The first gas is Gas A and the second gas is Gas B. Relative rate mean find the ratio v A /v B.

73 C. Johannesson 2.) A molecule of oxygen gas has an average speed of 12.3 m/s at a given temp and pressure. What is the average speed of hydrogen molecules at the same conditions? C. Grahams Law Problems Put the gas with the unknown speed as Gas A.

74 C. Johannesson 3.) An unknown gas diffuses 4.0 times faster than O 2. Find its molar mass. C. Grahams Law Problems The first gas is Gas A and the second gas is Gas B. The ratio v A /v B is 4.0. Square both sides to get rid of the square root sign.

75 Gases VI. Gas Stoichiometry at Non-STP Conditions

76 A. Gas Stoichiometry b Moles Liters of a Gas: STP - use 22.4 L/mol Non-STP - use ideal gas law b Non- STP Given liters of gas? start with ideal gas law Looking for liters of gas? start with stoichiometry conv.

77 B. Volume Mass Stoich. b Thinking: Gas volume A moles A moles B mass B b If gas A is at STP: ? L A 1 mol A ? mol B molar mass(g) B 22.4 L A ? mol A 1 mol B Mole Ratio

78 B. Volume Mass Stoich. b If gas A is NOT at STP: Use PV = nRT to find moles of A ? mol A ? mol B molar mass (g) B ? mol A 1 mol B

79 C. Johannesson WORK: n = PV RT n= (97.3 kPa) (15.0 L) (8.315 dm 3 kPa/mol K ) (294K) n = mol O 2 B. Volume Mass 1.) How many grams of Al 2 O 3 are formed from 15.0 L of O 2 at 97.3 kPa & 21°C? GIVEN: P = 97.3 kPa V = 15.0 L n = ? T = 21°C = 294 K R = dm 3 kPa/mol K 4 Al + 3 O 2 2 Al 2 O L non-STP ? g Given liters: Start with Ideal Gas Law and calculate moles of O 2. NEXT

80 2 mol Al 2 O 3 3 mol O 2 B. Volume Mass 1.) How many grams of Al 2 O 3 are formed from 15.0 L of O 2 at 97.3 kPa & 21°C? mol O 2 = 40.6 g Al 2 O 3 4 Al + 3 O 2 2 Al 2 O g Al 2 O 3 1 mol Al 2 O L non-STP ? g Use stoich to convert moles of O 2 to grams Al 2 O 3.

81 1 mol SO L SO 2 B. Volume Mass 2.) What mass of sulfur is required to produce 12.6 L of sulfur dioxide at STP according to the equation: S 8 (s) + 8 O 2 (g) 8 SO 2 (g) 12.6 L SO 2 = 18.0 g S g S 8 1 mol S L ? g 1 mol S 8 8 mol SO 2

82 C. Mass Volume b Thinking: Mass A moles A moles B gas volume B b If gas B is at STP: ? g A 1 mol A ? mol B 22.4 L B molar mass (g) A ? mol A 1 mol B

83 C. Mass Volume b If gas B is NOT at STP: ? g A 1 mol A ? mol B molar mass (g) A ? mol A Then use PV = nRT to find volume of B

84 C. Mass Volume 1.) What volume of chlorine gas at STP is needed to react completely with 10.4 g of sodium to form NaCl? 2 Na + Cl 2 2 NaCl 10.4 g ? L 10.4 g Na g Na 22.4 L Cl 2 1 mol Cl 2 2 mol Na 1 mol Cl 2 1 mol Na = L Cl 2

85 1 mol CaCO g CaCO 3 C. Mass Volume 2.) What volume of CO 2 forms from 5.25 g of CaCO 3 at 103 kPa & 25ºC? 5.25 g CaCO 3 = 1.26 mol CO 2 CaCO 3 CaO + CO 2 1 mol CO 2 1 mol CaCO g? L non-STP Looking for liters: Start with stoich and calculate moles of CO 2. Plug this into the Ideal Gas Law to find liters.

86 C. Johannesson WORK: V = nRT P V = (1.26mol)(8.315dm 3 kPa/mol K) (298K) (103 kPa) V = 30.3 dm 3 CO 2 C. Mass Volume 2.) What volume of CO 2 forms from 5.25 g of CaCO 3 at 103 kPa & 25ºC? GIVEN: P = 103 kPa V = ? n = 1.26 mol T = 25°C = 298 K R = dm 3 kPa/mol K


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