Daltons Law of partial pressures states that the total pressure in a mixture is

# Daltons law of partial pressures states that the

• Notes
• 50

This preview shows page 33 - 42 out of 50 pages.

Dalton’s Law of partial pressures states that the total pressure in a mixture is the sum of the partial pressures of the component gases. The partial pressure of a gas is proportional to its mole fraction: P A = X A x P total X A = n A n total Mixtures of Gases
5-34 Sample Problem 5.9 Applying Dalton’s Law of Partial Pressures PROBLEM: In a study of O 2 uptake by muscle at high altitude, a physiologist prepares an atmosphere consisting of 79 mole % N 2 , 17 mole % 16 O 2, and 4.0 mole % 18 O 2 . (The isotope 18 O will be measured to determine the O 2 uptake.) The pressure of the mixture is 0.75 atm to simulate high altitude. Calculate the mole fraction and partial pressure of 18 O 2 in the mixture. PLAN: Find X and P from P total and mol % 18 O 2 . 18 O 2 18 O 2 divide by 100 multiply by P total partial pressure P 18 O 2 mole % 18 O 2 mole fraction, X 18 O 2
5-35 Sample Problem 5.9 SOLUTION: = 0.030 atm P = X x P total = 0.040 x 0.75 atm 18 O 2 18 O 2 = 0.040 X 18 O 2 = 4.0 mol % 18 O 2 100
5-36 Collecting a water-insoluble gaseous reaction product and determining its pressure.
5-37 T ( 0 C) T ( 0 C) 0 5 10 12 14 16 18 20 22 24 26 28 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 55.3 71.9 92.5 118.0 149.4 187.5 233.7 289.1 355.1 433.6 525.8 633.9 760.0 4.6 6.5 9.2 10.5 12.0 13.6 15.5 17.5 19.8 22.4 25.2 28.3 31.8 42.2 Table 5.2 Vapor Pressure of Water ( P ) + at Different T H 2 O P (torr) H 2 O P (torr) H 2 O
5-38 Sample Problem 5.10 Calculating the Amount of Gas Collected over Water PLAN: The difference in pressures will give P for the C 2 H 2 . The number of moles ( n ) is calculated from the ideal gas law and converted to mass using the molar mass. PROBLEM: Acetylene (C 2 H 2 ) is produced in the laboratory when calcium carbide (CaC 2 ) reacts with water: CaC 2 ( s ) + 2H 2 O( l ) C 2 H 2 ( g ) + Ca(OH) 2 ( aq ) A collected sample of acetylene has a total gas pressure of 738 torr and a volume of 523 mL. At the temperature of the gas (23 o C), the vapor pressure of water is 21 torr. How many grams of acetylene are collected?
5-39 Sample Problem 5.10 multiply by M P total P of C 2 H 2 mass of C 2 H 2 use ideal gas law n of C 2 H 2 subtract P for H 2 O PLAN: SOLUTION: P C 2 H 2 = (738 - 21) torr = 717 torr 1 atm 760 torr = 0.943 atm P = 717 torr x 1 L 10 3 mL = 0.523 L V = 523 mL x T = 23°C + 273.15 K = 296 K
5-40 = 0.0203 mol 0.0203 mol x 26.04 g C 2 H 2 1 mol C 2 H 2 = 0.529 g C 2 H 2 SOLUTION: Sample Problem 5.10 0.943 atm 0.523 L x atm·L mol·K 0.0821 x 296 K n C 2 H 2 = RT PV =
5-41 Kinetic-Molecular Theory - How It Explains the Gas Laws Rationalize Five Key Questions at Molecular Level 1.Origin of Pressure. How do individual gas particles create P? 2.Boyle’s Law – V α1/P. What happens to particles when subjected to P?