CHM 1045
Dr. Michael Blaber

Name_________________________

SS #__________________________

Exam #4 100 points total

  1. Name three characteristics of gasses which distinguishes them from solids or liquids (6 points)

    2. a. Gasses expand to fill the volume of their container (have no defined shape or volume)

    b. Gasses can be compressed

    c. Gasses form homogenous mixtures with each other regardless of identity or properties

    d. Individual molecules are relatively far apart

    e. The kinetic energy of gas molecules is significantly greater than intermolecular attractive forces

  2. At the top of Mount Everest a 1m2 column of air has a mass of 7,300 kg. What is the atmospheric pressure on the top of Mount Everest? (5 points)

    3. P = F/A

    F = mass * acceleration = 7,300 kg * 9.78 m/s2 = 71.4 x 103 kg m/s2 = 71.4 x 103 N

    P = 71.4 x 103 N / 1 m2 = 71.4 x 103 Pa or 71.4 kPa

     

  3. What is the pressure, in atmospheres, of the gas in the following open-tube manometer? Assume that atmospheric pressure is 102 kPa. (5 points)

    4. 102 kPa (1 atm / 101 kPa) = 1.01 atm

    27 mm Hg (1 atm / 760 mm Hg) = 0.0355 atm

    Pressure = 1.01 – 0.0355 = 0.975 atm OR 98.5 kPa

     

  4. A 7.31 liter sample of gas at 50° C and 2.82 atm of pressure is subsequently compressed to 0.546 liters. In response to being compressed, the temperature increases to 72° C. What is the pressure of the gas after this compression? (5 points)

    5. P1V1/T1 = P2V2/T2

    P2 = (T2/V2) * (P1V1/T1) = (273+72 K)/(0.546 L) * (2.82 atm * 7.31 L)/(273+50 K)

    P2 = 632 K/L * 0.0638 atm L/K = 40.3 atm

  5. A small balloon holds 0.823 L of gas at standard temperature and pressure. How many moles of gas are in the balloon? (5 points)

    6. PV = nRT, therefore, n = PV/RT = (1 atm * 0.823L)/(0.0821 L atm/mol K * 273 K)

    n = 0.0367 moles or 3.67 x 10-2 moles

  6. What is the volume of a 5.7 mol sample of gas at 0.0231 atm pressure at 3° C? (5 points)

    7. PV = nRT

    V = nRT/P = 5.7 mol * 0.0821 L atm /mol K * (273+3) / 0.0231 atm

    V = 5591 L or 5.59 x 103 L

     

  7. What is the density of Carbon dioxide gas at 1.83 atm and 42°C? (5 points)

    8. CO2 = 12 + (2*16) = 44 g/mol

    d = PM/RT = (1.83 atm * 44 g/mol)/(0.0821 L atm/mol K * (273+42 K))

    d = 3.11 g/L

     

  8. An artificial atmosphere for the planet Jupiter consists of 92% hydrogen and 8% helium. 15g of this gas mixture are placed in a 50L container at –25°C. What is the partial pressure of each gas? (5 points) What is the mole fraction of hydrogen and helium in the artificial atmosphere? (5 points)

    9. Hydrogen (H2): (15g * 0.92)(1 mol/2.02g) = 6.83 mol

    Helium (He): (15g * 0.08)(1 mol/4.00g) = 0.3 mol

    PV = nRT

    P = nRT/V

    P(H2) = 6.83 mol * 0.0821 mol L/atm K * (273-25K) / 50L = 2.78 atm

    P(He) = 0.3 mol * 0.0821 mol L/atm K * (273-25K) / 50L = 0.122 atm

    Mole fraction Hydrogen = 6.83/(6.83+0.3) = 0.958

    Mole fraction Helium = 0.3/(6.83+0.3) = 0.042

  9. A car runs on propane (C3H8) gas and has a tank with a volume of 210L. How many grams of propane will the tank hold if it can be pressurized to 3.25 x 103 kPa at 30°C? (5 points)

    10. 3.25 x 103 kPa (1 atm/101 kPa) = 32.2 atm

    PV = nRT

    n = PV/RT = 32.2 atm * 210L / 0.0821 L atm/mol K * 303K = 272 moles

    272 moles (44 g/mol) = 12.0 x 103 g or 12.0 kg

  10. In question #9, if the car burn through an entire tank full of propane, how many grams of water are produced? (5 points)

    11. C3H8 + 5O2 -> 3CO2 + 4H2O

    272 moles C3H8 * (4 mol H2O/1mol C3H8) = 1088 mol H2O

    1088 mol H2O * (18g / mol) = 19,600 g or 19.6 kg

  11. A box contains 4 molecules of Carbon dioxide. Their individual velocities are 64.7, 23.8, 4.9 and 39.6 m/s. What is the average kinetic energy (in Joules) of these gaseous molecules? (5 points)

    12. RMS velocity = ((64.72+23.82+4.92+39.62)/4)1/2 = 39.8 m/s

    Ek = ½ * (44 amu)*(1.66 x 10-24 g/amu) * (39.8 m/s)2

    Ek = 5.78 x 10-20 g m2/s2 = 5.78 x 10-23 kg m2/s2 = 5.78 x 10-23 J

     

  12. What is the rate of diffusion for a molecule of diatomic oxygen compared to a molecule of carbon dioxide? (5 points)

    13. r1/r2 = (M2/M1)1/2

    rO2/rCO2 = (44 g/mol /32 g/mol)1/2 = 1.17

    diatomic oxygen diffuses 1.17 times faster than carbon dioxide

      

  13. Van der Waals constants for water are a = 5.46 L2 atm/mol2 and b= 0.0305 L/mol. Calculate the pressure exerted by 2.8 g of water vapor at 125° C in a container with a volume of 5.3L (5 points)

    14. T = 273 + 125 = 398 K

    2.8g H2O * 1 mol/18g = 0.156 mol

  14. What is the enthalpy change associated with the heating of 53g of H2O from 250K to 400K? (10 points)

    15. 53 g * (1mol/18g) = 2.94 moles

    heating of ice from 250K to 273K = 2.09 J/gK * (23K) * 53g = 2.55 kJ

    fusing ice to water = 6.01 kJ/mol * 2.94 moles = 17.7 kJ

    heating water from 273K to 373K = 4.18 J/gK * (100K) * 53g = 22.2 kJ

    vaporizing liquid water to gas = 40.67 kJ/mol * (2.94 mol) = 120 kJ

    heating water vapor from 373 to 400K = 1.84 J/g K * (27K) * 53g = 2.63 kJ

    total = 2.55 + 17.7 + 22.2 + 120 + 2.63 = 165 kJ

  15. Identify the changes in processes indicated in the following phase diagram (6 points)

    16. A. Sublimation

    B. Condensation

    C. Fusion (melting)

     

  16. The critical temperature of H2O is 647.6 K and the critical pressure is 217.7 atm. A).What state of H2O would you expect at 650K and 10,000 atm? B). What state would you expect at 645K and 220 atm? (5 points)

    17. A. Gas

    B. Liquid

  17. In the lattice diagram below, draw a border around a unit cell and indicate an asymmetric unit of the unit cell (5 points)

    18.  

    The blue indicates two possible unit cells. The red indicates an asymmetric unit

  18. What type of attractive interactions would allow Noble gas atoms to condense into the liquid phase? (3 points)

London dispersion forces