# 4. Gas Laws Questions

1. A bottle of soft drink contains a small amount of gas above the liquid at a pressure of 150 kPa. If the pressure of the atmosphere is 98 kPa, and the inside diameter of the neck of the bottle is 15 mm, calculate the net force on the bottle cap                                                            [9.2 N]
2. A bulb has a mass of 126.453 g when evacuated, 204.937 g when filled with water of density 0.9975 g/cm3, and 127.297 g when filled with a sample of a gaseous compound. Wha tis the density of the gas?                 [0.0107 g/cm3]
3. A sample of gas is compressed to 1/3 of its original volume and the temperature is increased from 15℃ to 145℃. Calculate the ratio of the final pressure to the initial pressure.                              [4.35]
4. The volume of a sample of gas is reduced to 1/4 of its original volume and the temperature is increased from 15℃ to 80℃. Calculate the ratio of final density to initial density.                            
5. In a diesel engine, air is heated by rapid compression. suppose that air is taken into the cylinder at a pressure of 95 kPa and 27℃ and compressed into 1/10 of its original volume. After compression the pressure of the air is measured to be 2500 kPa. Calculate the temperature in Kelvins of the compressed air.                                       [790 K]
6. Calcium hydride, CaC2(s), reacts with water to produce calcium hydroxide Ca(OH)2, and hydrogen gas.  Write a balanced equation for the reaction. Calculate ethe volume of hydrogen gas measured at 100 kPa and 298 K, which would be produced by the reaction of 27.3 g of calcium hydride.  [3.89 L]
7. Consider two identical bulbs, containing gas at equal temperatures and equal pressures.  one bulb contains pure phosphine, PH3(g) and the other pure hydrogen sulfide, H2S(g). Assuming the gases are ideal, which weighs more?  which bulb contains more molecules? Which tank contains more atoms?
8. The mole fraction of CO2 is 0.036% in normal air, and about 4% in exhaled air. If a person breathes 10 L of air per minute, what mass of CO2 is being produced per minute?             [0.7 g]
9. Calculate the density of methane at 20. ℃ and 250. kPa.                 [1.64 g/mL]
10. A sample of 100. mL of oxygen at 750. torr is mixed iwth 200. mL of nitrogen at a pressure of 500. torr and the mixture is transferred to a 150 mL vessel. The temperature is constant throughout the procedure.  Calculate the total pressure and the partial pressures of each gas after mixing.
[1167torr, 500 torr O2, 667 torr N2]
11. The time required for a given volume of nitrogen to effuse through a tiny hole is 35 s.  Calculate the molar mass of a gas which requires 50. s for the same volume of gas to effuse through the same hole under the same conditions.                        [57g/mol]
12. 64.0 g of gaseous ethane, C2H6, is placed in a 33.0 L bulb at 27.0℃.
1. What is the pressure of the gas [161 kPa]
2. Strong ultraviolet light is shone on the gas and 56% of the ethane molecules are converted to ethyne (acetylene). C2H2, and hydrogen H2. write a balance equation to show the decomposition reaction
3. Calculate the pressure in the bulb after the decomposition, assuming the temperature is held constant at 27.0 ℃.  [342 kPa]
13. in normal operation, a mass spectrometer is pumped down to a very low pressure of 2.5×10-4Pa.  Calculate the number of air molecules per cubic centimeter in the remaining gas if the temperature is 24 ℃.
[6×1010 molecules/cm3]
14. Air bags are now being fitted as safety equipment in cars.  Many airbags are inflated with nitrogen gas generated by the rapid reaction of sodium azide, Na3N(s), and iron oxide, Fe2O3(s).  The products of the reaction are sodium oxide, metallic iron and gaseous nitrogen. Write a balanced equation for the reaction and calculate the mass of sodium azide required to provide 75 L of gas at 25 ℃ and 120. kPa.                   [157 g]
15. Carbon dioxide vapour in equilibrium with liquid carbon dioxide at a temperature of 20.0 ℃ has a molar volume of 227 mL/mol.  Calculate the pressure of the gas under these conditions using the ideal gas equation and the van der Waals equation. Compare your results with the experimental pressure of 5.73 MPa.                        [10.7 MPa, 6.14 MPa] 