ENGR 1540 Worksheet 21 Chapter 5
1. During a collision, automobile air bags are inflated by the N2 gas formed by the explosive decomposition of sodium azide, NaN3: 2NaN3→2Na+3N2 What mass of sodium azide would be needed to inflate a 30.0-L bag to a pressure of 1.40 atm at 25℃?
2. You want to store 165 g of CO2 gas in a 12.5-L tank at room temperature (25℃). Calculate the pressure the gas would have using
a. the ideal gas law
b. the van der Waals equation
(For CO2, a=3.59 atm L2/mol2 and b=0.0427 L/mol.)
3. Liquid oxygen for use as a rocket fuel can be produced by cooling dry air to -183℃, where the O2 condenses. How many liters of dry air at 25℃ and 750 torr would need to be processed to produce 150 L of liquid O2 at -183℃? (The mole fraction of oxygen in dry air is 0.21, and the density of liquid oxygen is 1.14 g/mL.)
4. A number of compounds containing the heavier noble gases, and especially xenon, have been prepared. One of these is xenon hexafluoride (XeF6), which can be prepared by heating a mixture of xenon and fluorine gases. XeF6 is a white crystalline solid at room temperature and melts at about 325 K. A mixture of 0.0600 g of Xe and 0.0304 g of F2 is sealed into a 100.0-mL bulb. (The bulb contains no air or other gases.) The bulb is heated, and the reaction goes to completion. Then the sealed bulb is cooled back to 20.0℃. What will be the final pressure in the bulb, expressed in torr?
5. You work in a semiconductor production plant that relies on several chlorofluorocarbons in its manufacturing process. One day, you find an unlabeled gas cylinder, and you are assigned to figure out what is in the tank. First, you fill a 1.000-L flask with the gas. At a pressure of 250.0 torr and a temperature of 25.00℃, you determine that the mass of the gas in the flask is 2.2980 g. Then, you send the flask to an outside lab for elemental analysis, and they report that the gas contains 14.05% C, 44.46% F, and 41.48% Cl by mass. Find the molecular formula of this gas.
6. A 0.2500-g sample of an Al-Zn alloy reacts with HCl to form hydrogen gas:
The hydrogen produced has a volume of 0.1447 L at 25℃ and 755 mm Hg. What is the percentage of zinc in the alloy?
7. A mixture of Ar (0.40 mol), O2 (0.50 mol), and CH4 (0.30 mol) exerts a pressure of 740 mm Hg. If the methane and oxygen are ignited and complete combustion occurs, what is the final pressure of Ar, CO2, H2O, and the remainder of the excess reactant? What is the total pressure of the system?
8. The complete combustion of octane can be used as a model for the burning of gasoline: 2C8H18+25O2→16CO2+18H2O Assuming that this equation provides a reasonable model of the actual combustion process, what volume of air at 1.0 atm and 25℃ must be taken into an engine to burn 1 gallon of gasoline? (The partial pressure of oxygen in air is 0.21 atm, and the density of liquid octane is 0.70 g/mL.)
9. Mining engineers often have to deal with gases when planning for the excavation of coal. Some of these gases, including methane, can be captured and used as fuel to support the mining operation. For a particular mine, 2.4 g of CH4 is present for every 100.0 g of coal that is extracted. If 4 5.6% of the methane can be captured and the daily production of the mine is 580 metric tons of coal, how many moles of methane could be obtained per day?
10. Some engineering designs call for the use of compressed air for underground work. If water containing iron(II) ions is present, oxygen in the compressed air may react according to the following unbalanced net ionic equation: Fe2++H++O2→Fe3++H2O
a. Write the balanced net ionic equation. Remember that the amounts of each substance and the charges must balance.
b. Assume all of the oxygen from 650 L of compressed air at 15℃ and 6.5 atm is lost by this reaction. What mass of water would be produced? (The mole fraction of oxygen in air is about 0.21.)
c. What will be the final pressure after the loss of the oxygen?
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