Chemistry Gases: Worksheet p. 3
§ 11.HW / Gases: WorksheetMost Important Ideas: Write the gas laws (Dalton, Combined, Avogadro’s, Ideal, Graham’s)
1 atm = 760 mm Hg = 760 mm torr = 14.7 psi = 101.325 kPa
Expected Outcome
At the conclusion of this worksheet, you will be able to solve problems dealing with the physical properties of gases, such as determining:
(a) the amount of a specific gas produced by a chemical reaction, and the amount of reactants needed to produce that amount (Dalton’s Law);
(b) the volume of a gas bubble as it rises from the bottom of a lake to the top, where it bursts (Combined Gas Law);
(c) the pressure inside a balloon and the molar mass of a gas (two forms of the Ideal Gas Law);
(d) the relative rate that two gases escape from a common container (Graham’s Law).
References
Textbook (Modern Chemistry, 2012). Chapter 11: Gases. (pp. 340-377).
Water Vapor Pressure
Temperature, °C / Pressure, mm Hg / Temperature, °C / Pressure, mm Hg0 / 4.6 / 40 / 55.3
5 / 6.5 / 50 / 92.5
10 / 9.2 / 60 / 149.4
15 / 12.8 / 70 / 233.7
20 / 17.5 / 80 / 355.1
23 / 21.1 / 90 / 525.8
25 / 23.8 / 95 / 633.9
30 / 31.8 / 100 / 760.0
35 / 42.2
Problems
§11.01 – Introduction, Pressure, Gas Laws Overview, Dalton’s Law
· Read section 11-1; do practice problems (pp.345, 347).
1. The total pressure of a mixture of H2, He, and Ar is 99.3 kPa. The partial pressure of the He is 42.7 kPa and the partial pressure of Ar is 54.7 kPa. What is the partial of the hydrogen gas expressed in: (a) kPa, (b) atm, (c) mm Hg, (d) torr, and (e) psi?
2. The pressure of a tire for an 18-wheeler truck is approximately 85 psi. Convert this to (a) atm; (b) mm Hg, (b) torr, (c) kPa.
3. What is the formula used to calculate pressure?
4. The partial pressures of a gas mixture are 0.55 atm CH4, 0.44 atm C2H6, and 0.51 atm C3H8. What is the total pressure of the mixture?
5. The atmospheric composition by volume of Neptune is mostly 80% H2, 19% He, 1.5% CH4. What is the partial pressure of each gas given the total atmospheric pressure is equal to the pressure found at sea level on Earth?
6. A sample of nitrogen gas is collected over water at a temperature of 23oC. What is the pressure of the nitrogen gas if the atmospheric pressure is 785 mmHg?
7. A CO2 gas sample is collected over water at a temperature of 25.0oC at 105.33 kPa. What is the partial pressure of the CO2?
Extension
8. A 2.00-g sample of sodium hydrogen carbonate is completely decomposed. The gases are collected over water and allowed to cool to 0oC at 760 mm Hg pressure.
a. Write the balanced chemical equation.
b. How many moles of each gas are produced?
c. The two sources of water in the gas sample (i) from the decomposition of the sodium hydrogen carbonate, and (ii) the vapor pressure of water, merely by collecting the gas sample by water displacement. Calculate the partial pressure of both ‘dry’ gases produced from the decomposition reaction.
d. What is the partial pressure of each gas (CO2 and H2O) produced from the reaction?
e. What is the partial pressure of the total H2O vapor? (Hint: Add together the pressure of the water produced by the reaction and the water vapor released simply by being collected over water.)
§11.02 The Combined Gas Law
· The Combined Gas Law is made by combining three gas laws: Boyle’s, Charles’s, and Gay-Lussac. We combine them to make one equation that covers all three.
· Read section 11-2. Do practice problems (pp.350, 352, 353-4, 355).
1. What is the equation for the combined gas law? What does each variable represent? What temperature scale do you have to use? (Note: In the calculations, if you’re not given a variable, such as number of moles, assume it doesn’t change.)
N.B. When solving combined gas law problems, it helps a lot to use the following table to keep the initial and final conditions organized.
P1 = P2 =
V1 = V2 =
n1 = n2 =
T1 = T2 =
2. A sample of oxygen gas has a volume of 150. mL when the pressure is 0.947 atm. What will the volume of the gas be at 0.987 atm if the temperature remains constant?
3. A sample of neon gas occupies a volume of 752 mL at 25˚C. What temperature will the gas have at a volume of 543 mL if the pressure remains constant?
4. A helium filled balloon has a volume of 50.0 L at 25.0˚C and 1.08 atm. What pressure (kPa) will it have at a volume of 75.0 L and -10.0˚C?
5. The volume of a gas at 27.7˚C and 250. mm Hg is 80.0 mL. What volume will the gas have at STP?
6. Major Sean Heenan, 10th Mountain Division, fills his Humvee tires to 30.0 PSI at Ft. Drum NY in January when the temperature was –10.0 ˚C. He is shipped out to Kandahar Afghanistan and arrives in May with the temperature at 35.0˚C. What is the tire pressure in PSI in Kandahar?
7. (A) A meteorological balloon contains 250.L He at 22oC and 740 mm Hg. Assuming the volume of the balloon is flexible, what would the volume be at an altitude where the temperature is –52oC and the pressure is 0.750 atm?
Extension
8. A 2.0-L balloon is filled with nitrogen gas at STP. As the balloon rises, the pressure and temperature drop to 670 mm Hg and –10oC. A small hole is detected which has allowed the volume of the balloon to drop by 252 mL. How many grams of nitrogen gas have escaped?
9. The normal inhalation respiratory rate for a human being is 15.0 breaths/min. The average volume of each breath is 505 cm3 at 20oC and 9.95 x 104 Pa. What is the volume of air (STP) that an individual inhales in one day? Give your answers in cubic meters.
§11.03 Gas Volumes and the Ideal Gas Law
· Avogadro’s Law: Equal volumes of gases (at the same T & P) contain the same number of molecules. {Because all of the molecules in these conditions have the same kinetic energy, the pressure each gas exerts is equal to its percent of the total number of moles.)
· Read section 11-3 (pp. 359-365). Do practice problems (pp.361, 362, & 365).
1. A sample of nitrogen gas kept in a 2.3-L container at 32oC exerts a pressure of 4.7 atm. Calculate the number of moles of gas present.
2. Given that 6.9 moles of carbon monoxide gas are present in a 30.4 L container, what is the pressure (atm) if the temperature is 62oC?
3. What volume will 5.6 moles of sulfur hexafluoride gas occupy if the temperature is 128oC and the pressure is 9.4 atm?
4. What is the temperature of 4.0 moles of 12-L of gas at 5.6 atm?
5. How many atoms of oxygen are present in a 2.5 L flask of oxygen gas at 50°C and 650 mm Hg?
6. Dry ice is solid carbon dioxide. A 0.050-g sample of dry ice is placed in an evacuated 4.6-L vessel at 30oC. Calculate the pressure inside the vessel after all of the dry ice has been converted to gas.
7. How many grams of carbon tetrachloride occupy a 55-L vessel at STP?
8. The ozone molecules (O3) in the stratosphere absorb much of the harmful radiation from the sun. Typically, the temperature and pressure of ozone in the stratosphere are 250 K and 10–3 atm, respectively. How many ozone molecules are present in 1.0 L of the stratosphere?
9. Calculate the density of HBr gas in grams per liter at 733 mmHg and 46oC.
- A certain anestheticcontains 64.9 percent C, 13.5 percent H, and 21.6 percent O by mass. At 120oC and 750 mm Hg, 1.00 L the gas weighs 2.30g. What is its molecular formula?
Extension
- A sample of a solvent used in nail polish remover is placed in a 3.00-L flask and vaporized by heating to 95oC at 1.02 atm. The vapor filling the flask at this temperature and pressure weighs 5.87 g.
a. What is the density of this gas at these conditions?
b. Calculate the molar mass of the solvent.
c. This solvent contains C, H, and O. When 1.000-g is burned, 2.27 g of CO2 and 0.932 g of H2O are formed. What is the molecular formula of the solvent?
§11.04 Diffusion and Effusion
· Read section 11-4 (pp. 366-369). Do practice problems (p.368) & Math Tutor (p. 369)
1. List the following gases in order of increasing average molecular velocity:
· H2O
· He
· HCl
· BrF
· NO2
2. If neon gas travels at 40.0 m/s, calculate the velocity of butane gas (C4H10) at the same temperature.
3. What is the diffusion rate of nitrogen gas if helium gas diffuses at 1.00 cm/s?
4. Which diffuses faster, ammonia (NH3) or helium gas? What is the relative rate of diffusion of NH3 compared to He?
5. What is the molecular weight of a gas which diffuses 1/50 as fast as hydrogen?
6. Under the same conditions of temperature and pressure, how many times faster will hydrogen gas effuse compared to carbon dioxide gas?
7. In the summer of 2013, the NYPD reportedly released two gases in the subway system to see how gaseous materials travel there. One of the reported gases was sulfur hexafluoride, which traveled at 2.50 cm/s. The unknown gas traveled at 1.58 cm/s. (a) What was the molar mass of the second gas? (b) If the empirical formula is CF2, what is the molecular formula of this compound?
8. A sample of hydrogen gas diffuses through a porous container 4.3 times faster than an unknown gas. Estimate the molar mass of that gas and name the gas.
9. Ammonia has an average gas velocity of 175 m/s. Compare that to the velocity of hydrogen chloride gas at the same temperature and pressure.
10. Ammonia (NH3) and hydrogen chloride are each placed on a small piece of cotton, which are placed at either ends of a 100-cm glass tube. Both liquids are very volatile and the gases will react where they meet, forming solid ammonium chloride (NH4Cl). At what distance, from either end of the tube, will the two gases meet?
Extension
11. Two porous containers are filled with H2 and Ne, respectively. Under identical conditions, two-thirds of the H2 escapes in six hours. How long will it take for one-half of the neon to escape?