Chapter 5 Gases Kinetic Theory All matter is composed of tiny particles that are in continuous, random motion. Gas Pressure = Force Demo: Test tube/h2o beaker Area Demo: Can AP CHEMISTRY Chapter 5 Scotch Plains-Fanwood High School Page 1
1 atm = 760 mmhg = 760 torr = 101.3 kpa = (14.7 lb/in 2 ) Remember last year s graph of V vs. p of gas with the piston and books AP CHEMISTRY Chapter 5 Scotch Plains-Fanwood High School Page 2
2 Condition Problems Design your own formula 1. 2. 3. 4. 5. p 1 V1 n1 T1 = p2 V2 n2 T2 Just match units on both sides, but ALWAYS USE KELVIN! If a 2.0 L balloon has a Boyle s Law p1v1 = p2v2 pressure of 3.0 atm, find the pressure if the volume is 1.0 L. Charles Law V1 = V2 If a balloon has a volume T1 T2 of 10.0 L at 30. C, find the Gay-Lussac s Law p1 = p2 temperature at which it T1 T2 would have a volume of 20.0 L. Combined Gas p1v1 = p2v2 If the pressure in a Law T1 T2 helium tank is 2.0 atm at Avogadro s Law V1 = V2 20. C, find the pressure at 30. C. n1 n2 If a 16.0 L balloon at 40. C has a pressure of 600. mm Hg, find the volume it would have at 500. mm Hg and 50. C. If a 24.0 L balloon has 9.0 mol of gas, what volume would it occupy with 18.0 mol of gas? AP CHEMISTRY Chapter 5 Scotch Plains-Fanwood High School Page 3
1 Condition Problems IDEAL conditions p V = n R T Ideal Gas Law pv=nrt p = press in atm n = moles V = Vol in L R = 0.0821 Latm/molK T = Temp in K 1. Find the pressure in a 20.0 L tank containing 5.0 moles of carbon dioxide at 30.0 C. 2. Find the volume needed for 16.0 grams of O2 at 40.0 C and 54.0 kpa. MM = drt MM = Molar Mass in g/mol d = density in g/l p p = press in atm R = 0.0821 Latm/molK T = Temp in K 3. Find the density of F2 gas at 12.0 C and 800. mm Hg. AP CHEMISTRY Chapter 5 Scotch Plains-Fanwood High School Page 4
Dalton s Law of Partial Pressures # Students Mole Fraction Total Pressure MF x TP = PP Partial Pressure 50 Chem Mole Fraction 30 Bio 20 Phys Total Pressure (mm Hg) Partial Pressure (mm Hg) A B If all the physics students leave # Students Mole Fraction Total Pressure Partial Pressure 50 Chem 30 Bio Gas Mole Fraction Total Pressure (kpa) Partial Pressure (kpa) O2 N2 Ar H2O CO2 AP CHEMISTRY Chapter 5 Scotch Plains-Fanwood High School Page 5
Kinetic Energy of Gases (depends ONLY on T) KE = 3/2 (R T) n [R = 8.31 J/molK] 1. Find the KE of 1 mole of carbon dioxide gas at 25 C. 2. Find the KE of 1 mole of hydrogen gas at 25 C. 3. Find the KE of 2 moles of hydrogen gas at 25 C. Root Mean Square Velocity of Gases (depends on T and MM) μrms = 3RT [R = 8.31 J/molK] MM [Molar Mass is in kg!!!!] 1. Find the μrms of carbon dioxide gas at 25 C. 2. Find the μrms of hydrogen gas at 25 C. AP CHEMISTRY Chapter 5 Scotch Plains-Fanwood High School Page 6
Graham s Law of Effusion and Diffusion Rate1 = MM2 Time1 = MM1 Rate2 MM1 Time2 MM2 1. Find the ratio of the rates of diffusion of carbon dioxide gas and hydrogen gas. 2. If hydrogen gas takes 20.0 min to effuse from a balloon, how long would it take carbon dioxide to effuse from an identical balloon? Question: How would you collect a sample of gas exhaled by a person? AP CHEMISTRY Chapter 5 Scotch Plains-Fanwood High School Page 7
Collecting a gas over water 1. Oxygen gas is produced according to the (unbalanced) equation below and collected over water: (The vapor pressure of water at 27.0 C is torr.) KClO3(s) KCl(s) + O2(g) How many grams of potassium chlorate must be decomposed in order to produce 800. ml of oxygen at 27.0 C and 1.20 atm? 2. Oxygen gas is produced according to the (unbalanced) equation below and collected over water: (The vapor pressure of water at 29.8 C is torr.) KClO3(s) KCl(s) + O2(g) How many grams of potassium chlorate must be decomposed in order to produce 400. ml of oxygen at 29.8 C and 80.0 kpa? AP CHEMISTRY Chapter 5 Scotch Plains-Fanwood High School Page 8
AP CHEMISTRY Chapter 5 Scotch Plains-Fanwood High School Page 9
Partial Pressure worksheet MF x TP = PP 1. You are given 0.30 mol of H2, 0.10 mol of CO2, and 0.20 mol of He in a sealed container. The total pressure in the container is 988 mm Hg. Find the partial pressure of each gas. Gas # Moles Mole Fraction Total Pressure Partial Pressure (mm Hg) (mm Hg) H2 0.30 0.30 = 0.50 988 494 0.60 CO2 0.10 0.10 = 0.17 0.60 He 0.20 0.20 = 0.33 0.60 988 165 988 329 2. a. 8.00 g of He, 132 g of CO2, 2.00 g of H2, and 64.0 g of CH4 are combined in a closed tank. The pressure gauge of the tank registers 800. mm Hg. Find the partial pressure of each gas in the tank. Gas # grams # Moles Mole Fraction Total Pressure (mm Hg) Partial Pressure (mm Hg) He 8.00 2.00 2.00 = 0.200 10.00 800. 160. CO2 132 3.00 3.00 = 0.300 10.00 H2 2.00 1.00 1.00 = 0.100 10.00 CH4 64.0 4.00 4.00 = 0.400 10.00 800. 240. 800. 80.0 800. 320. b. If all the methane (CH4) is taken out of the tank, find the new mole fractions and partial pressures of the remaining gases. Gas # grams # Moles Mole Fraction Total Pressure (mm Hg) Partial Pressure (mm Hg) He 8.00 2.00 2.00 = 0.333 480. 160. 6.00 CO2 132 3.00 3.00 = 0.500 480. 240. 6.00 H2 2.00 1.00 1.00 = 0.167 6.00 480. 80.0 AP CHEMISTRY Chapter 5 Scotch Plains-Fanwood High School Page 10
Real vs. Ideal Gases Van der Waals Equation: Find the REAL pressure of 133 moles of methane gas at 26 C in a volume of 115.0 L. Compare this to the IDEAL pressure of methane under the same conditions. Compare a values of water and methane. Compare b values of xenon with helium. AP CHEMISTRY Chapter 5 Scotch Plains-Fanwood High School Page 11
Van der Waals Equation Practice worksheet Find the IDEAL pressure in a 250.0 L tank containing 80.0 g of helium at 19.0 C. Find the REAL pressure in a 250.0 L tank containing 80.0 g of helium at 19.0 C. NOTE: On page 11 the ideal and real pressures were more discrepant b/c of non-ideal conditions (low volume for relatively high moles resulting in high pressure), but on this page the ideal and real pressures are the same b/c of more ideal conditions (higher volume and lower moles resulting in relatively low pressure) AP CHEMISTRY Chapter 5 Scotch Plains-Fanwood High School Page 12