AP Chemistry                                                         Unit 6

Chapter 6                                                               Thermochemistry

 

1.   A piano is brought upstairs by two workers. Due to a mistake by one of the workers, the piano rolls down the stairs and finally comes to rest by the outside door. Which sequence best describes the energy transformations for the piano. (PE – potential energy, KE – kinetic energy, TE – thermal energy, GE – ground energy)

      a. PEàKEàTE of the ground and piano

      b. GEàPEàTEàKE of piano

      c. PEàKEàPEàTE of piano and ground

      d. KEàPEàKE

 

2. As a system increases in volume, it releases 52.5 J of energy in the form of heat to the surroundings. The piston it is working against has a pressure of 10.25 atm. The final volume of the system is 58 L. What was the initial volume if the energy of the system decreased by 102.5 joules

      a. 62.9 L

      b. 53.1 L

      c. 48 L

      d. 68 L

 

3. What is the final temperature in °C when 20.0 g of water at 80.0°C is mixed with 20.0 g water at 25°C

      a. 12°C

      b. 7.0°C

      c. 8.8°C

      d. 52.5°C

 

4. Silane SiH4 is highly combustable and creates a fire hazard

                              SiH4(g)  +  2O2(g)  à  SiO2(s) + 2H2O(g)  ΔH = ?

Calculate ΔH for this reaction based on the following

Si(s)  + 2H2(g) à  SiH4(g)                       ΔH= +34 kJ/mole

Si(s) + O2(g) à  SiO2(s)                   ΔH= -911kJ/mole

H2(g) +1/2 O2(g) à  H2O(g)  ΔH= -242 kJ/mole

 

5. How much heat will be evolved if 56.08 g of calcium oxide reacts with sulfuric acid according to the following reaction:

                  CaO(s)  +  H2SO4(g) à  CaSO4(s)  + H2O(l)

 

Given the following

Ca(s)  + ½ O2(g) à CaO(s)                          ΔH= -152 kJ/mole

Ca(s)  + S(s) + 2O2(g) à CaSO4(s)                 ΔH= -1434 kJ/mole

H2(g) ) + 1/2O2(g) à  H2O(l)             ΔH= -286 kJ/mole

H2(g) + S(s) +2O2(g) à H2SO4(g)                      ΔH= -814 kJ/mole

 

 

6. Calculate the heat of reaction for the following

                  2KIO3(s)  +  12HCl(g) à 2ICl(l)  + 2KCl(s) + 6H2O(l)  +  4Cl2(g)

 

given the respective heats of formation are

      -501.0 kj/mole, -92 kJ/mole, -24 kJ/mole, -435 kJ/mole, -286 kJ/mole

 

7. The carbon dioxide and water in our atmosphere have all the following effects except

      a. increasing average global temperatures

      b. allowing visible light to escape

      c. absorbing and trapping infrared radiation

      d. extending the length of summer days

 

8. A system does 3 J of work on the surroundings and 12 J of work are added to the system.

    1. What is the energy change of the system?
    2. Of the surroundings?

 

9. One hundred joules of work are required to compress a gas. At the same time, the gas gives off 23 J of heat to the surroundings. What is the energy change of the system?

 

10. A gas expands from 10 L to 20 L against a constant pressure of  5 atm. During this time it absorbs 2 kJ of heat. Calculate the work (and change in energy ΔE ) done in kJ.

 

11. A piston expands against 1.00 atm of pressure, from 11.2 L to 29.1 L. This is done without any transfer of heat.

    1. Calculate the change in energy of the system.
    2. Calculate the change in energy for the above change if, in addition, the system absorbs 1,037 J of heat from the surroundings.

 

12. If the internal energy of a thermodynamic system is decreased by 300 J when 75 J of work is done by the system, how much heat is transferred, and in which direction, to or from the system?

 

13. How much work is done by a system where pressure is kept constant, but the volume changes from 20 L to 0.5 L (100 atm)?

 

14. A gas is compressed against a constant pressure of 3.4 atm from 27.9 L to 16.3 L. During this process, there is a heat gain by the system of 122 J. calculate the change in energy of the system.

 

15. If 596 J of heat are added to 29.6 g of water at 22.9 degrees C in a coffee cup calorimeter, what will be the final temperature of the water?

 

16. A 5.037 g piece of iron heated to 100 degrees C is placed in a coffee cup calorimeter that initially contains 27.3 g of water at 21.2 degrees C. If the final temperature is 22.7 degrees C, what is the specific heat capacity of the iron (J/g degrees C)?

 

17. Calculate the heat necessary to convert 10.0 g of water (just melted) at 0 degrees C to water at 20 degrees C, assuming that the specific heat remains constant at 1 cal/g degrees C.

 

18. The specific heat of aluminum is 0.89 J/g degrees C. How much energy is required to raise the temperature of a 15.0 gram aluminum can 18 degrees C?

 

19. One liter of an ideal gas at 0 degrees C and 10 atm was allowed to expand to 1.89 L against a constant external pressure of 1 atm, at a constant temperature. 901 J are absorbed in the process by the system. Calculate q, w, and ΔE.

 

20. The heat capacity of a bomb calorimeter was determined by burning 6.79 g of methane (heat of combustion = -802 kJ/mol) in the bomb. The temperature changed by 10.8 degrees C.

 

a. What is the heat capacity of the bomb?

b. A 12.6 g sample of acetylene, C2H2, produced a temperature increase of 16.9 degrees C in the same calorimeter. What is the heat of combustion of acetylene (kJ/mol)?

 

21. A sample of C6H5COOH (benzoic acid) weighing 1.221 g was placed in a bomb calorimeter and ignited in a pure O2 atmosphere. A temperature rise from 25.24 degrees C to 31.67 degrees C was noted. The heat capacity of the calorimeter was 5. 020 kJ/degrees C and the combustion products were CO2 and H2O. Calculate the ΔH in kJ/mol for the reaction.

 

22. When 1.50 L of 1.00 M Na2SO4 solution at 30.0 degrees C is added to 1.50 L of 1.00 M Ba(NO3)2 solution at 30.0 degrees C in a calorimeter, a white solid (BaSO4) forms. The temperature of the mixture increases to 42.0 degrees C. Assuming that the specific heat capacity of the solution is 6.37 J/degrees C g and that the density of the final solution is 2.00 g/mL, calculate the enthalpy change per mole of BaSO4 formed.

 

23. Calculate ΔH for

                  N2(g) + O2(g)  à 2NO(g)

Given

N2(g) + 2O2(g) à2NO2(g)                   ΔH= -66.4 kJ

2NO(g)+ O2(g) à 2NO2(g)               ΔH= -114.1 kJ

 

24. For the reaction

                  H2O(l) à H2O(g)           ΔH= +44 kJ/mole

 

How much heat is involved when 9.0 g of water vapor is condensed to liquid water?

 

25. Calculate ΔH for

                  CH4(g) + 2O2(g) à CO2(g) + 2H2O(l)

 

Given

2H2(g) + C à CH4(g)                       ΔH= -74.81 kJ

2H2(g) + O2(g) à 2H2O(l)                ΔH= -571.66 kJ

C(s) + O2(g) à CO2(g)                      ΔH= -393.52 kJ

 

26. Determine ΔH for the following

                  Ca(s) + 2H2O(l) à  Ca(OH)2(s) + H2(g)

Given

H2(g) + ½ O2(g) à H2O(l)                               ΔH= -285 kJ

CaO(s) + H2O(l) à Ca(OH)2(s)                    ΔH= -64 kJ

Ca(s) + ½ O2(g) àCaO(s)                             ΔH= -635 kJ

                 

27. Use the standard change in enthalpy table (A4 in text) to calculate ΔH

2H2O2(l) à 2H2O(l) + O2(g)                         (ΔHf H2O2(l)= -187.8 kJ/mole)

HCl(g) à H+(aq) + Cl-(aq)

2NO2(g) à N2O4(g)

C2H2(g) +H2(g) à C2H4(g)

2NaOH(s) + CO2(g)à Na2CO3(s) + H2O(g)