Chem 107 Final Exam, Page 7 of 18 Dec 7, 2017 C. decrease D. depends on the pres

Question

Chem 107 Final Exam, Page 7 of 18 Dec 7, 2017 C. decrease D. depends on the pressure E. Not enough information is given to correctly answer the question. 26. A sample of hydrogen gas was collected over water at 21 C and 685 mmHg. The volume of the container was 7.80L. Caleulate the mass of H2(g) collected. (Vapor pressure of water = 18.6 mmHg at 21°C) A. 0.283g B. 0.389g C. 0.571g D. 7.14g E. 435g 27. Which statement is false? A. The average kinetic energies of molecules from samples of different "ideal" gases is the same at the same temperature. B. Molecules of greater mass have a lower average speed than those of less mass at the same temperature C. The molecules of an ideal gas are relatively far apart D. All molecules of an ideal gas have the same kinetic energy at constant temper- ature. E. Molecules of a gas undergo many collisions with each other and the container walls. 28. There are two tanks of equal volume at identical pressure and temperature. If one is filled with SF,(g) and the other is filled with CH4(g), which tank contains more gas A. Because the molar mass of SFe(g) is greater than that of CH(8), the SFols) B. Because the formula for CH4(g) contains fewer atoms, the CH, tank contains molecules? C. Because the CH4(8) molecule is smaller in size than the SFs(s) molecule, the D. Because each tank contains the same number of moles of gas, both tanks 29. (3 points) How much heat is required to raise the temperature of 2500g of water from tank contains more molecules. more molecules. CHs tank contains more molecules. contain the same number of molecules. 27 to 72°C? The specific heat of water is 4.184 J/g°C A. 931 k.J

Explanation / Answer

26. V = 7.8L
    T = 21^0C = 21+273 = 294K
    P = 685mmHg -18.6mmHg =666.4mmHg = 666.4/760 = 0.87atm
    PV = nRT
     n = PV/RT
       = 0.87*7.8/0.0821*294 = 0.285moles
mass of H2 = no of moles * gram molar mass
             = 0.285*2 = 0.571g
C. 0.571g
27. The kinetic energy of gas is directley proportioanl to absolute temperatue.
   D >>>>answer
28.from avogadro's law
   D>>>>>answer
29. q = mcDT
       = 2500*4.184*(72-27)
       = 470700J    = 470.7KJ>>>>>answer  

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