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# Gases

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1. Gases Chapter 5

2. Properties of Gases • Gases form homogeneous mixtures • Gases are compressible • All gases have low densities • air 0.0013 g/mL • water 1.00 g/mL • iron 7.9 g/mL • Gases expand to fill their containers uniformly • A gas exerts a pressure

3. Pressure • Defined as force per unit area

4. Pressure Units • 101.325 kPa • = 760 mmHg • =760 torr • =1 atm • =30 in Hg • =14.7 psi

5. The atmospheric pressure is 638 torr. What is the pressure in atmospheres?

6. The Gas Laws • Boyles Law P 1/V • Charles Law V  T • Avogadros Law V  n • Combined gas law P nT/V

7. Ideal Gas Law PV = nRT • P = pressure (typical units are atm or torr or mm Hg) • V = volume (typical units are L) • n = number of moles • T = temperature (must be in K) • R = gas constant = 0.0821 L atm/mol K • = 62.4 L torr/mol K

8. The nitrogen gas in an air bag with a volume of 35 L, exerts a pressure of 850 mm Hg at 25oC. How many grams of N2 are in the bag?

9. How many moles of helium are found in a balloon that contains 5.5 L of helium at a pressure of 1.15 atm and a temperature of 22.0 ºC? • 3.5 • 0.26 • 2.6 • 0.35 • 3.8

10. Standard Temperature and Pressure (STP) 1 atm pressure and 00C Calculate the density of Argon gas at STP

11. How many moles of helium are found in a balloon that contains 5.5 L of helium at a pressure of 1.15 atm and a temperature of 22.0 ºC? • 3.5 • 0.26 • 2.6 • 0.35 • 3.8

12. Helium-filled balloons are used to carry scientific instruments high into the atmosphere. Suppose that a balloon is launched when the temperature is 22.5oC and the barometric pressure is 754 mm Hg. If the balloon’s volume is 4.19 x 103 L, what will it be at a height of 20 miles, where the pressure is 70.0 mm Hg and the temperature is 33.0oC?

13. Gaseous oxygen reacts with aqueous hydrazine to produce water and gaseous nitrogen according the balanced equation N2H4(aq) + O2(g)  2 H2O(l) + N2(g). If a solution contains 180 g of N2H4, what is the maximum volume of O2 that reacts with the hydrazine if the O2 is measured at a barometric pressure of 750 mm Hg and room temperature (21oC)?

14. Gaseous ammonia is synthesized from nitrogen and hydrogen by the reaction N2(g) + 3 H2(g) 2 NH3(g) with an iron catalyst at 500oC. If you take 355 L of H2 gas at 25oC and 542 mmHg and combine it with excess N2 what volume of NH3 gas will be collected under the same conditions?

15. A mixture of CO(g) and O2(g) in a 2.89 L container at 907K has a total pressure of 2.75 atm. After time, the pressure falls to 2.24 atm due to CO2 formation. How many grams of CO2 are formed?

16. Daltons Law of Partial Pressures • Ptotal = P1 + P2 + P3 + ...... + Pn

17. Halothane has the formula C2HBrClF3. It is a nonflammable, non-explosive, and non-irritating gas that is a commonly used inhalation anesthetic. Suppose you mix 15.0 g of haloethane vapor with 23.5 g of oxygen gas, if the total pressure of the mixture is 855 mmHg, what is the mole fraction of each gas? What is the partial pressure of each gas?

18. A mixture of Ar and N2 gases has a density of 1.413 g/L at STP. What is the mole fraction of each gas?

19. Vapor Pressure • The partial pressure of a gas in equilibrium with liquid.

20. A sample of nitrogen gas is collected over water at 15oC. If the barometric pressure in the laboratory is 747 mmHg, what is the partial pressure of the dry nitrogen gas in the sample?

21. Acetylene may be produced from the reaction between calcium carbide and water. How many moles of acetylene are present in a 500.0 mL sample of gas collected over water at 20.0 ºC and a total pressure of 758 torr? The vapor pressure of water at 20.0 ºC is 17.54 mm Hg. • 0.0207 • 0.0203 • 15.4 • 0.297 • 0.304

22. Acetylene may be produced from the reaction between calcium carbide and water. How many moles of acetylene are present in a 500.0 mL sample of gas collected over water at 20.0 ºC and a total pressure of 758 torr? The vapor pressure of water at 20.0 ºC is 17.54 mm Hg. • 0.0207 • 0.0203 • 15.4 • 0.297 • 0.304

23. Dichlorine oxide is a powerful oxidizing agent that is used to bleach wood pulp and to treat municipal water supplies. It is made by the reaction SO2(g) + 2 Cl2(g)  SOCl2(g) + Cl2O(g). If you put SO2 in a flask so that its pressure is 125 mmHg at 22oC, and if you add Cl2 gas to this same flask, what should the Cl2 partial pressure be in order to have the correct stoichiometric ratio of SO2 to Cl2?

24. Kinetic Molecular Theory • Gases consist of molecular particles moving in straight lines at any given instant.

25. Kinetic Molecular Theory • Molecules collide with each other and the container walls without any net loss of energy.

26. Kinetic Molecular Theory • Gas molecules behave independently -- attractive/repulsive forces between them are negligible.

27. Kinetic Molecular Theory • Gas molecules are widely spaced, the actual volume of molecules is negligible compared to the space they occupy.

28. Kinetic Molecular Theory • The average kinetic energy of the gas particles is proportional to the temperature.

29. The four most common gases in the atmosphere are N2, O2, Ar, and CO2. Which gas has the highest average kinetic energy at room temperature? • N2 • O2 • Ar • CO2 • All have the same average kinetic energy

30. The four most common gases in the atmosphere are N2, O2, Ar, and CO2. Which gas has the highest average kinetic energy at room temperature? • N2 • O2 • Ar • CO2 • All have the same average kinetic energy

31. Kinetic Molecular Theory • Gases consist of molecular particles moving in straight lines at any given instant. • Molecules collide with each other and the container walls without any net loss of energy. • Gas molecules behave independently -- attractive/repulsive forces between them are negligible. • Gas molecules are widely spaced, the actual volume of molecules is negligible compared to the space they occupy. • The average kinetic energy of the gas particles is proportional to the temperature.

32. The four most common gases in the atmosphere are N2, O2, Ar, and CO2. Assuming all gases are in containers of equal size, temperature, and pressure, which gas has the highest density? • All have the same density • N2 • O2 • Ar • CO2