ChemBytes - Chapter 5

Answers

CHEMBytes: Additional Problems on Gases

  1. A certain sample of gas has a volume of 0.452 L measured at 87°C and 0.620 atm. What is its volume at 1 atm and 0°C? 0.212 L
  2. Calculate the number of moles in a sample of an ideal gas whose volume is 0.452 L at 87°C and 0.620 atm? 0.00948 moles
  3. An ideal gas at 1 atm pressure was contained in a bulb of unknown volume V. A stopcock was opened which allowed the gas to expand into a previously evacuated bulb whose volume was known to be exactly 0.500 L. When equilibrium between the bulbs had been established, it was noted that the temperature had not changed, and that the gas pressure was 530 torr. What was the unknown volume V of the first bulb? 1.15 L
  4. It is found that 0.896 g of a gaseous compound containing only nitrogen and oxygen occupies 524 mL at a pressure of 730 torr and a temperature of 28.0°C. What is the molecular weight and molecular formula of the gas? 43.9 g/mol; probably N2O
  5. Ethylene reacts with hydrogen in the presence of a platinum catalyst (according to the equation that follows), forming ethane:
    C2H4(g) + H2(g) —> C2H6(g)
    A mixture of C2H4(g) and H2(g) known only to contain more H2 than C2H4 had a pressure of 52 torr in an unknown volume. After the gas had been passed over the catalyst bed its pressure was 34 torr in the same volume and at the same temperature. What fraction of the molecules in the original mixture was ethylene? 35%
  6. A gaseous compound known to contain only carbon, hydrogen, and nitrogen is mixed with exactly the volume of oxygen required for the complete combustion to CO2, H2O, and N2. Burning 9 volumes of the gaseous mixture produces 4 volumes of CO2, 6 volumes of water vapor, and 2 volumes of N2, all at the same temperature and pressure. How many volumes of oxygen are required for the combustion? What is the molecular formula of the compound? C2H4N2
  7. The valve between a 5-L tank in which the gas pressure is 9 atm and a 10-L tank containing a gas that is at 6 atm is opened, and the pressure equilibrium ensues at constant temperature. What is the final pressure in the two tanks? 7 atm
  8. A sample of PCl5 weighing 2.69 g was placed in a 1.00 L flask and completely vaporized at a temperature of 250°C. The pressure observed at this temperature was 1.00 atm. The possibility exists that some of the PCl5 may have dissociated according to the equation
    PCl5 (g) = PCl3 (g) + Cl2 (g)
    What are the partial pressures of PCl5, PCl3, and Cl2 under these experimental conditions? Respectivley, 0.106 atm, 0.447 atm, and 0.447 atm
  9. Calculate the root-mean-square speed (in cm/s and at 25°C) of a free electron and of a molecule of UF6. vrms(electron) = 1.17x107cm/s; vrms(UF6) = 1.45x104cm/s
  10. Compare the root-mean-square speed (at 20°C) of He and the escape velocity of earth. Given the information in ChemByte 4, what do you conclude? vrms(He at 20° C) = 1.35x105cm/s; escape velocity = 11.2x105cm/s
  11. A mixture of hydrogen and helium is prepared such that the number of wall collisions per unit time by molecules of each gas is the same. Which gas has the higher concentration? Helium