GENERAL CHEMISTRY I
CHEM 1311.001
EXAM 3
Friday November 14, 1997

Name___________________________

SSN____________________________

Note: Some (but not all) problems on this exam require the use of the universal gas constant R. For your information note that it's value is as follows:

R = 0.08205783 (L atm) / (K mol)

1. A gas was confined in a cylinder fitted with a movable piston. At 11.22 oC, the gas occupied a volume of 1.407 L and exerted a pressure of 1.179 atm. The gas was then isobarically heated, causing it to expand (lifting the piston higher in the cylinder). After the heating process, the gas occupied a volume of 1.957 L. What was the temperature of the gas after the heating? For full credit, you must express your final answer in Celcius (oC). (Hints: Note that the process is isobaric. Also, assume that the cylinder does not leak, and no chemical reaction takes place in the gas, so that the number of moles will be constant.)

2. A gas was confined in a closed, rigid steel tank having a volume of 4.953 L. At 15.81 oC, the gas exerted a pressure of 1.935 atm. If the gas is heated to a temperature of 99.48 oC, what pressure will it exert? (Hints: Since the gas is in a closed, rigid steel tank, its volume will be constant. Also assume the tank does not leak, and no chemical reaction takes place in the gas, so that the number of moles will be constant).

3. A gas was confined in a cylinder fitted with a movable piston. At 21.52 oC, the gas occupied a volume of 3.774 L and exerted a pressure of 1.506 atm. The gas was isothermally compressed (by pushing in the piston) until the gas pressure was 2.713 atm. What volume did the gas occupy after the compression? (Hints: Note that the process is isothermal. Also assume the cylinder does not leak, and no chemical reaction takes place in the gas, so the number of moles will be constant).

4. A gas was confined in a cylinder fitted with a movable piston. At 17.31 oC, the gas occupied a volume of 1.957 L and exerted a pressure of 2.154 atm. The gas was simultaneously heated and compressed. After the heating and compression, the gas had a temperature of 66.51 oC and occupied a volume of 1.218 L. What pressure did the gas exert under these conditions?

5. A steel tank contains 9.173 g of nitrogen gas (N2) at 22.84 oC. The gas exerts a pressure of 4.183 atm. What is the volume of the tank? Atomic weights needed to work this problem are as follows:

N = 14.00674

6. A steel tank having a volume of 5.906 L contains 6.817 g of methane gas (CH4) at 26.19 oC. What pressure does the methane exert? Atomic weights needed to work this problem are as follows:

H = 1.00794 and C = 12.011

7. A steel tank having a volume of 3.584 L contains 5.831 g of ammonia gas (NH3). The gas pressure is 2.431 atm. What is the temperature of the gas? For full credit, your final answer must be expressed in Celcius (oC). Atomic weights needed to work this problem are as follows:

H = 1.00794 and N = 14.00674

8. What is the density of propane gas (C3H8) at 27.50 oC and 1.007 atm? Atomic weights needed to solve this problem are as follows:

H = 1.00794 and C = 12.011

9. What is the meaning of the term "isochoric"?

10. What two gas parameters must be constant in order to use Charles' Law? You must identify both to receive full credit.

ANSWERS

1)   122.38 oC       2)   2.495 atm       3)   2.095 L       4)   4.047 atm       5)   1.901 L      

6)   1.767 atm       7)   36.96 oC       8)   1.800 g / L

9)   Isochoric means the volume is constant

10)   Gas pressure and number of moles must be constant to use Charles' Law

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