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May 138:16 PM
States of Matter
Review
Sep 136:04 PM
Solid Liquid
Gas Freezing
Melting
Evaporation
Condensation
SublimationDeposition
Physical States of Matter (Phases)
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May 138:11 PM
May 127:52 PM
GasesChapter 12
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May 812:58 PM
Gases fill their container completely.
Gases can be
compressed.
Gases have
mass.
Properties of Gases
Gases are fluids.
Gases have low density.
Gases move from high to low pressure
May 812:56 PM
Properties of GasesDiffusion: the ability of a gas to move through another substance;
• Molecules move towards areas of lower concentration until equilibrium is reached and the concentration is uniform throughout the system. • High Pressure to Low Pressure• Ex: opening a bottle of perfume • Ex: adding food dye to water
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May 812:56 PM
Properties of Gases
Effusion: ability of a gas to move through a tiny hole (rate gases escape)
Gases with lower molecular masses effuse and diffuse ___________ than gases with higher molecular masses.
Graham's Law: Relates Rates of effusion (or diffusion) to molar masses
May 154:40 PM
Simulation Activity
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May 812:48 PM
KineticMolecular Theory of Gases
Kinetic Theory: all submicroscopic particles in are constant, random motion; the E of these particles is called Kinetic Energy.
KMT describes the motion of gases:
1. Gases are made from tiny particles called molecules. (Mostly empty space that allows the gas to be compressed)
2. Gas molecules are in constant, rapid, straightline motion & posses kinetic energy.
KE = ½ mv2
The motion is interrupted by collisions with other molecules & walls of the container.
This causes pressure (a force exerted on a unit area of a surface).
May 812:48 PM
3. These collisions are elastic (won’t lose energy). Total energy remains constant as long as the temperature and volume don’t change.
4. Gas molecules display no attraction or repulsion for each other.
5. The molecules have different velocities but it is assumed that the average kinetic energy is proportional to the absolute temperature of the gas.
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May 81:01 PM
Four Measurable Quantities Of A Gas
1. Moles, n amount of substance 6.02 x 1023 molecules =1 mole
2. Volume,V amount of space a gas will occupy
1 mole of any gas at STP has a volume of 22.4L
Units 1cm3 = 1 mL 1000 mL = 1 L
Ex. 2.16 mol/L = ? mol/ cm3
May 81:08 PM
Avogadro’s Hypothesis Equal volumes of any gases contain an equal number of particles.
1 mole takes up 22.4 L of space at STP. ***only true for gases
When tightly packed, larger molecules take up more space
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May 81:02 PM
3. Temperature, T the average kinetic energy of the particles in a sampleUnits oC = Celsius *Used to take measurements in lab
K = Kelvin *Used to calculate data Kelvin Scale: K = oC + 273 IMPORTANT Temps• Absolute Zero: the temperature at which there is no particle movement. At absolute zero, KE = 0; theoretically; no one has ever reached it (0 Kelvin)• 0oC = H2O Freezing/Melting pt. & Standard Temp.• 100oC = H2O Boiling/Condensation pt
May 81:03 PM
4. Pressure, P (Force over an area) caused by the molecular collisions on the walls of the container. Units1.00atm = 101.3kPa = 760mmHg = 760 torr =14.7psi
Ex. 2.19 kPa = ? Torr
Ex. 5.2 atm = ? mmHg
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May 81:04 PM
Atmospheric pressure pressure caused by molecules in the earth’s atmosphere
• Measured using a manometer or barometer
May 81:21 PM
Mixtures of Gases
Dalton’s Law of Partial Pressure • The total pressure of a mixture of gases is equal to the sum of the partial pressures of all the gases.
Ptotal = Pa + Pb + Pc +…. Petc
• The partial pressure of each gas is equal to the mole fraction of each gas x total pressure.
Pa = XaPtotal
Xa =
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Dec 2310:07 AM
Daltons' Law of Partial Pressures
PTotal = Pa + Pb + Pc ...
Pa = XaPtotal
Xa =
May 81:21 PM
Ex. 1 Air contains oxygen, nitrogen, carbon dioxide, and trace amounts of other gases. What is the partial pressure of oxygen (PO2) at 101.20 kPa of pressure if PN2 = 79.10 kPa, Pco2 = 0.040 kPa, and Pothers = 0.94 kPa?
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May 81:21 PM
Ex. 2 In a gas mixture of 2 moles water vapor and 5 moles nitrogen gas, what is the pressure caused by the N2 gas if the total pressure in the flask is 800. mmHg?
May 81:22 PM
A common method of collecting gas during an experiment is by trapping it "over water." An inverted bottle filled with water sits in a water bath. A tube from the reaction vessel transfers the gas into the bottle where it bubbles to the top and displaces water, which runs out the mouth of the bottle into the water bath.However, there is an unavoidable problem. The gas saturates with water vapor and now the total pressure inside the bottle is the sum of two pressures the gas itself and the added water vapor.
WE DO NOT WANT THE WATER VAPOR PRESSURE.
So we get rid of it by subtraction. This means we must get the water vapor pressure from somewhere.We get it from a table because the water vapor pressure depends only on the temperature, NOT how big the container is or the pressure of the other gas. Usually the textbook will have an abbreviated table with more complete tables in reference manuals like "The Handbook of Chemistry and Physics."
Ex 3. 0.750 L of a gas is collected over water at 23.0°C with a total pressure of 99.75 kPa. What is the pressure of the dry gas?
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May 81:22 PM
0 0.61129 35 5.6267 70 31.1761 0.65716 36 5.9453 71 32.5492 0.70605 37 6.2795 72 33.9723 0.75813 38 6.6398 73 35.4484 0.81359 39 6.9969 74 36.9785 0.8726 40 7.3814 75 38.5636 0.93537 41 7.784 76 40.2057 1.0021 42 8.2054 77 41.9058 1.073 43 8.6463 78 43.6659 1.1482 44 9.1075 79 45.48710 1.2281 45 9.5895 80 47.37311 1.3129 46 10.094 81 49.32412 1.4027 47 10.62 82 51.34213 1.4979 48 11.171 83 53.42814 1.5988 49 11.745 84 55.58515 1.7056 50 12.344 85 57.81516 1.8185 51 12.97 86 60.11917 1.938 52 13.623 87 62.49918 2.0644 53 14.303 88 64.95819 2.1978 54 15.012 89 67.49620 2.3388 55 15.752 90 70.11721 2.4877 56 16.522 91 72.82322 2.6447 57 17.324 92 75.61423 2.8104 58 18.159 93 78.49424 2.985 59 19.028 94 81.46525 3.169 60 19.932 95 84.52926 3.3629 61 20.873 96 87.68827 3.567 62 21.851 97 90.94528 3.7818 63 22.868 98 94.30129 4.0078 64 23.925 99 97.75930 4.2455 65 25.022 Source: Handbook of 31 4.4953 66 26.163 Chemistry & Physics: 73rd32 4.7578 67 27.347 Edition (1992-93)33 5.0335 68 28.57634 5.3229 69 29.852
May 81:21 PM
Ex. 4 Hydrogen gas is collected over water at a total pressure of 95.0 kPa. The volume of hydrogen collected is 28 mL at 25oC. What is the partial pressure of hydrogen gas? (Use the CRC’s table with vapor pressure data for water.)
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May 81:08 PM
The Gas Laws
3 steps for solving gas law problems
1. Write down all the givens with the correct variable and units.2. Isolate or solve for the variable of interest.3. Plug in all the numbers making sure the units agree (cross out) and that temperature is in Kelvin. Apply sig. figs.
May 81:11 PM
Ex 1P1 = 1 atmV1 = 50 mLP2 = 2 atmV2 = ?
Boyles' Law: With constant temp and # of moles, pressure and volume of a gas are inversely proportional
Ex. 2 A car piston as a volume of 10.8 mL when the pressure is .972 atm. If the piston is forced down so the volume is only .00251 L, what would the new pressure inside the piston be?
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May 81:14 PM
Charles' Law: With pressure and moles of gas constant, volume and absolute temperature are directly proportional.
Ex. 1T1 = 25oCV1 = 30. mLV2 = 25 mLT2 = ?
Ex. 2 If a balloon had a volume of 20.6 mL inside a room at 22oC, what would its volume be outside on a cold day of 25oC?
May 81:16 PM
GayLussac’s Law At constant volume, the pressure of a fixed amount of gas varies directly with the Kelvin temperature.
Ex. 1 A gas confined to a container exerts a pressure of 33.5kPa at a temperature of 17.0oC. What will the pressure of this gas be if it is cooled to a temperature of 23.0oC?
Ex. 2 A quantity of gas exerts a pressure of 98.6 kPa at a temperature of 22oC. If the volume remains unchanged, what pressure will it exert at 8.0oC?
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Dec 239:50 AM
Combine Gas Lawmoles kept constant
Ex. A sample of oxygen gas has a volume of 205 mL when its temperature is 22.0oC and its pressure is 30.8 kPa. What volume will the gas occupy at STP.
May 81:17 PM
Ideal Gas Lawrelates all 4 measurable quantities of a gas. (there is no “change,” so there are no subscripts)
PV = nRT
Solve for RExactly 1 mole of gas takes up a space of 22.4L at STP.
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Dec 2310:13 AM
Ex: What is the density of CO2 gas at 771 torr and 28oC?
