Class Work, Homework, and TEST GRADE RECOVERY

Name ______Date ______Period

Class Work, Homework, and TEST GRADE RECOVERY

Chapter 5: Thermochemistry

Exercises: Sections 5.5: Calorimetry

1. How is heat flow determined?

2. Define the following:

(a) calorimetry

(b) calorimeter

3. (a) Define a spontaneous process.

(b) How are the enthalpies of a chemical reactions related to their spontaneity?

Combustion reactions are NOT spontaneous because they must be started with an input

of energy - such as striking a match.

4. The decomposition of potassium chlorate proceeds spontaneously when it is heated.

2KClO3(s) → 2KCl(s) + 3O2(g) ΔH = ─ 89.4 kJ

(a) Do you think that the reverse reaction, the formation of potassium chlorate from potassium chloride

and oxygen, is likely to be feasible under ordinary condition? Explain your answer.

(b) Suppose solid KCl was introduced into an oxygen-rich chamber and then the oxygen was ignited -

would the reverse reaction become spontaneous? Explain.

5. Define the following:

(a) heat capacity

(C)

(b) molar heat capacity

(Cm)

(Cs)

6. (a) What is the mathematical equation for the specific heat of a substance?

(b) Rearrange this equation to solve for the amount of heat transferred to or from a substance.

7. Consult the Table 5.2 on page 181 of the textbook to answer this question. Which of the substances in Table

5.2 will undergo the greatest temperature change when the same mass of each substance absorbs the same

quantity of heat? Justify your answer.

8. Two solid objects, A and B, are placed in boiling water and allowed to come to temperature there. Each is

then lifted out and placed in separate beakers containing 1000 g of water at 10.0oC. Object A increases the

water temperature by 3.50oC; B increases the water temperature by 2.60oC.

(a) Which object has the larger heat capacity? Explain.

(b) What can you say about the specific heat of A and B?

9. (a) Which substance in Table 5.2 on page 181 requires the smallest amount of energy to increase the

temperature of 50.0 g of that substance by 10 K? Explain.

(b) How is ΔT determined?

(d) Could problem 9(b) have been solved using Celsius instead of Kelvin temperatures? Explain.

10. (a) The specific heat of toluene, C7H8, is 1.13 J/ g-K. How many joules of heat are needed to raise the

temperature of 40.0 g of toluene from 10.4oC to 28.0oC? Follow ALL math work rules!

11. (a) Why is a simple coffee-cup calorimeter sufficient to measure ΔH?

(b) Identify the following for a simple coffee-cup calorimeter

(i) the system

(ii) the surroundings

(d) Are the assumptions from 11(c) reasonable? Explain.

12. (a) When a 4.25-g sample of solid ammonium nitrate dissolves in 60.0 g of water in a coffee-cup

calorimeter (Figure 5.18 on page 185 of the textbook), the temperature drops from 22.0oC to 16.9oC.

Calculate ΔH (in kJ/ mol NH4NO3) for the solution process

NH4NO3(s) → NH4+(aq) + NO3¯(aq)

Assume that the specific heat of the solution is the same as that of pure water. Follow ALL math work rules!

(b) How are the energy changes of a system and its surroundings related?

13. When 50.0 mL of 0.100 M AgNO3 and 50.0 mL of 0.100 M HCl are mixed in a constant-pressure

calorimeter, the temperature of the mixtures changes from 22.30oC to 23.11oC.

(a) Write a balanced chemical equation for this reaction.

(b) Based on ΔT, is this reaction exothermic or endothermic?

100.0 g and a specific heat of 4.18 . Follow ALL math work rules!

14. (a) What is a bomb calorimeter?

(b) Is bomb-calorimetry a constant-pressure process?

(d) Briefly describe the concept behind measuring heat flow in a bomb-calorimeter.

15. Suppose that the gas-phase reaction 2 NO (g) + O2 (g) → 2 NO2 (g), were carried out in a constant-

volume container at constant temperature.

(a) Would the measured heat change represent ΔH or ΔE?

(b) Explain

16. A 1.800-g sample of octane was burned in a bomb calorimeter whose total heat capacity is 11.66 kJ/ oC.

The temperature of the calorimeter plus contents increased from 21.36oC to 28.78oC.

(a) Write a balanced chemical equation for the bomb calorimeter reaction.

(b) What is the heat of combustion in kJ per gram of octane? Follow ALL math work rules!

17. Under constant-volume conditions the heat of combustion of benzoic acid, HC7H5O2, is 26.38 kJ/ g. A

1.200-g sample of benzoic acid is burned in a bomb calorimeter. The temperature of the calorimeter

increases from 22.45oC to 26.10oC.

(a) What is the total heat capacity of the calorimeter? Follow ALL math work rules!

(b) If the calorimeter in 17 (a) contained 1.500 kg of water, what is the heat capacity of the colorimeter

when it contains no water?