States of Matter Review May 13 8:16 PM Physical States of Matter (Phases) Solid Liquid Melting Gas Condensation Freezing Evaporation Deposition Sublimation Sep 13 6:04 PM 1
May 13 8:11 PM Gases Chapter 12 May 12 7:52 PM 2
Properties of Gases Gases have mass. Gases can be compressed. Gases are fluids. Gases have low density. Gases fill their container completely. Gases move from high to low pressure May 8 12:58 PM Properties of Gases Diffusion: 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 May 8 12:56 PM 3
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 8 12:56 PM Simulation Activity May 15 4:40 PM 4
Kinetic Molecular 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, straight line motion & posses kinetic energy. KE = ½ mv 2 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 8 12:48 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. May 8 12:48 PM 5
Four Measurable Quantities Of A Gas 1. Moles, n amount of substance 6.02 x 10 23 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 1cm 3 = 1 ml 1000 ml = 1 L Ex. 2.16 mol/l =? mol/ cm 3 May 8 1:01 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 May 8 1:08 PM 6
3. Temperature, T the average kinetic energy of the particles in a sample Units o C = Celsius *Used to take measurements in lab K = Kelvin *Used to calculate data Kelvin Scale: K = o C + 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) 0 o C = H 2 O Freezing/Melting pt. & Standard Temp. 100 o C = H 2 O Boiling/Condensation pt May 8 1:02 PM 4. Pressure, P (Force over an area) caused by the molecular collisions on the walls of the container. Units 1.00atm = 101.3kPa = 760mmHg = 760 torr =14.7psi Ex. 2.19 kpa =? Torr Ex. 5.2 atm =? mmhg May 8 1:03 PM 7
Atmospheric pressure pressure caused by molecules in the earth s atmosphere Measured using a manometer or barometer May 8 1:04 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. P total = P a + P b + P c +. P etc The partial pressure of each gas is equal to the mole fraction of each gas x total pressure. P a = X a P total X a = May 8 1:21 PM 8
Daltons' Law of Partial Pressures P Total = P a + P b + P c... P a = X a P total X a = Dec 23 10:07 AM Ex. 1 Air contains oxygen, nitrogen, carbon dioxide, and trace amounts of other gases. What is the partial pressure of oxygen (PO 2 ) at 101.20 kpa of pressure if PN 2 = 79.10 kpa, Pco 2 = 0.040 kpa, and P others = 0.94 kpa? May 8 1:21 PM 9
Ex. 2 In a gas mixture of 2 moles water vapor and 5 moles nitrogen gas, what is the pressure caused by the N 2 gas if the total pressure in the flask is 800. mmhg? May 8 1:21 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? May 8 1:22 PM 10
0 0.61129 35 5.6267 70 31.176 1 0.65716 36 5.9453 71 32.549 2 0.70605 37 6.2795 72 33.972 3 0.75813 38 6.6398 73 35.448 4 0.81359 39 6.9969 74 36.978 5 0.8726 40 7.3814 75 38.563 6 0.93537 41 7.784 76 40.205 7 1.0021 42 8.2054 77 41.905 8 1.073 43 8.6463 78 43.665 9 1.1482 44 9.1075 79 45.487 10 1.2281 45 9.5895 80 47.373 11 1.3129 46 10.094 81 49.324 12 1.4027 47 10.62 82 51.342 13 1.4979 48 11.171 83 53.428 14 1.5988 49 11.745 84 55.585 15 1.7056 50 12.344 85 57.815 16 1.8185 51 12.97 86 60.119 17 1.938 52 13.623 87 62.499 18 2.0644 53 14.303 88 64.958 19 2.1978 54 15.012 89 67.496 20 2.3388 55 15.752 90 70.117 21 2.4877 56 16.522 91 72.823 22 2.6447 57 17.324 92 75.614 23 2.8104 58 18.159 93 78.494 24 2.985 59 19.028 94 81.465 25 3.169 60 19.932 95 84.529 26 3.3629 61 20.873 96 87.688 27 3.567 62 21.851 97 90.945 28 3.7818 63 22.868 98 94.301 29 4.0078 64 23.925 99 97.759 30 4.2455 65 25.022 Source: Handbook of 31 4.4953 66 26.163 Chemistry & Physics: 73rd 32 4.7578 67 27.347 Edition (1992-93) 33 5.0335 68 28.576 34 5.3229 69 29.852 May 8 1:22 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 25 o C. What is the partial pressure of hydrogen gas? (Use the CRC s table with vapor pressure data for water.) May 8 1:21 PM 11
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 8 1:08 PM Boyles' Law: With constant temp and # of moles, pressure and volume of a gas are inversely proportional Ex 1 P 1 = 1 atm V 1 = 50 ml P 2 = 2 atm V 2 =? 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? May 8 1:11 PM 12
Charles' Law: With pressure and moles of gas constant, volume and absolute temperature are directly proportional. Ex. 1 T 1 = 25 o C V 1 = 30. ml V 2 = 25 ml T 2 =? Ex. 2 If a balloon had a volume of 20.6 ml inside a room at 22 o C, what would its volume be outside on a cold day of 25 o C? May 8 1:14 PM Gay Lussac 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 17.0 o C. What will the pressure of this gas be if it is cooled to a temperature of 23.0 o C? Ex. 2 A quantity of gas exerts a pressure of 98.6 kpa at a temperature of 22 o C. If the volume remains unchanged, what pressure will it exert at 8.0 o C? May 8 1:16 PM 13
Combine Gas Law moles kept constant Ex. A sample of oxygen gas has a volume of 205 ml when its temperature is 22.0 o C and its pressure is 30.8 kpa. What volume will the gas occupy at STP. Dec 23 9:50 AM Ideal Gas Law relates all 4 measurable quantities of a gas. (there is no change, so there are no subscripts) PV = nrt Solve for R Exactly 1 mole of gas takes up a space of 22.4L at STP. May 8 1:17 PM 14
Ex: What is the density of CO 2 gas at 771 torr and 28 o C? Dec 23 10:13 AM 15