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CHEM 120 Gases and ThermoChemistry - Full Solutions

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2. A 11.4-L cylinder contains 29.2g N2 at 71.0°C. What is the pressure of this gas, in atmospheres?
Answer: 2.58atm

3. A 31.0-L cylinder contains 407g O2(g) at 23.5°C. What mass of O2(g) must be released to reduce the pressure in the cylinder to 2.82atm, assuming the temperature remains constant?
Answer: 292 g

4. What is the density of Ar gas (molar mass, 39.95 g mol-1) at 32.1oC and 105 kPa? Give your answer in grams per litre (g L-1).
Answer: 1.65g/L

5. Carbon monoxide, CO, and hydrogen, H2, react according to the reaction below.
6CO(g) + 13H2(g) --> C6H14(g) + 6H2O(g)
What volume of the excess reactant remains if 19L CO and 40.8L H2 are allowed to react. Assume that the volumes of both gases are measured at 739°C and 1.27atm.
Answer: 0.16L

6. Calculate the volume of H2(g), measured at 23.5°C and 745 Torr required to react with 28.1L CO(g), also measured at 23.5°C and 745 Torr. Assume the gases react as follows.
Answer: 65.6L

7. One method of removing CO2(g) from a spacecraft is to allow the CO2 to react with LiOH. What volume, in liters, of CO2(g) at 26.3°C and 763 Torr can be removed by 1.11kg LiOH?
Answer: 567L

8. When solid NH4ClO4 decomposes, a mixture of gases is obtained:
2NH4ClO4(s) ---> 4H2O(g) + Cl2(g) + 2O2(g) + N2(g)
In an experiment, 2.41g NH4ClO4 decomposes completely in a rigid 2.25L container. What is the total pressure in the container if the final temperature is 243°C?
Answer: 1.54atm

9. A 1.7L flask of H2(g) at 1.5atm and a 4.8L flask of He(g) at 3.6atm are connected by a tube of negligible volume. A valve on the tube is opened, allowing the gases to mix at constant temperature with no reaction. What is the final pressure?
Answer: 3.1atm

10. If 0.00552mol N2O(g) effuses through an orifice in a certain period of time, how many moles of NO(g) would effuse in the same time under the same conditions?
Answer: 0.00669

11. Brass has a density of 8.40g/cm^(3) and a specific heat of 0.385Jg^(-1)°C^(-1). A 15.7cm^(3) piece of brass at an initial temperature of 174°C is dropped into an insulated container with 186.3 grams of water initially at 21.8°C. What will be the final temperature of the brass-water mixture? [The specific heat of water is 4.184Jg(-1)°C(-1).]
Answer: 31.1°C

12. What is w when the volume of a gas expands from 18.5L to 31.5L against a constant external pressure of 757mmHg? (Remember to include a "+" or "-" sign as appropriate.)
Answer: -1.31*10^(3)J

13. What is w when 2.61kg of H2O(l), initially at 25.0°C, is converted into water vapour at 141°C  against a constant external pressure of 1.00atm? Assume that the vapour behaves ideally and that the density of liquid water is 1.00g/mL.
Answer: -499kJ

14. What is the internal energy change for the system if 801 joules of heat flows into the system from the surroundings and 697 joules of work is done on the system by the surroundings?
Answer: 1498J

15. A sample of gas absorbs exactly 535J of heat from its surroundings. At the same time, the gas expands from 4.63L to 11.81L against a constant external pressure of 0.847atm. What is the internal energy change for the gas? Give your answer in joules (J).
Answer: -81.2J
*Don't forget that 1 atm L is not equal to 1 J. (1 atm L = 101.325 J)

16. A 0.008705-mol sample of an organic compound was burned in oxygen in a bomb calorimeter. The temperature of the calorimeter increased from 24.9°C to 31.0°C. If the heat capacity of the calorimeter is 4.68 kJ/°C, then what is the constant volume heat of combustion of this compound, in kilojoules per mole?
Answer: -3.28*10^(3)kJ/mol

17. The enthalpy change for the reaction below at 25°C is -1,850 kJ (per mole of C9H20). What is the internal energy change for the reaction at 25°C?
9CO(g) + 19H2(g) --> C9H20(l) + 9H2O(l)
Answer: -1781kJ (per mole of  C9H20)

18. The standard enthalpy change for the reaction below is -5005.0 kJ (per mol C10H8). What is the standard enthalpy of formation of C10H8(s)?
C10H8(s) + 12O2(g) --> 10CO2(g) + 4H2O(l)
Answer: -73.6 kJ/mol

19. Given the following thermochemical equations,
H2(g) + (1/2)O2(g) --> H2O(l) -285.9 kJ (per mol H2O)
C3H4(g) + 4 O2(g) --> 3CO2(g) + 2H2O(l) -1937.0 kJ (per mol C3H4)
C3H8(g) + 5 O2(g) --> 3CO2(g) + 4H2O(l) -2219.1 kJ (per mol C3H8)
what is the standard enthalpy change for the reaction below?
C3H4(g) + 2 H2(g) --> C3H8(g)
Answer: -289.7 kJ (per mol C3H4)


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