Thermochemistry:  Triptik for Chapter 8

Thermochemistry is the name given to the study of the energy changes that accompany chemical reactions and changes in the physical states of matter.

Section 8-1

1. Why do you suppose that the law of conservation of energy is said to be one of the most fundamental laws of science?

2. Define and compare kinetic energy and potential energy. Include the mathematical formulas for each and give the meaning for each part of the formulas.

3. Interpret Figure 8-2 in writing.

4. At what point is the KE = 0? (K.E. means the same as Ek, and what I prefer to use to represent kinetic energy.) What happens to the K.E. when the ball hits the ground?

5. The rate at which energy is produced is called power. What is the SI unit of power? How is it defined? Why does it represent a derived unit?

6. See if you can look at the electric bill for your home for July or August and then for last January or February. Write down the electricity usage and the unit cost.

7. What percentage of the electrical usage of those months would be met by the solar collector in Example 8-2?

8. Work Problems 8-1, 8-3, and 8-5.

Section 8-2

9. Distinguish between the reaction system and the surroundings.

10. How is energy transferred between the system and its surroundings?

11. What is required for work to be done? Write down how it is expressed mathematically.

12. For a system that is at constant P, compare the sign of work done on the system as a result of compression with that done on the system as a result of expansion.

13. Follow the solution to Example 8-3, then work Practice Problem 8-3.

14. Why does the transfer of energy as heat not require the application of a force?

15. In what direction does energy flow? What symbol is used to represent this?

16. How is the energy of a system denoted? Explain how DU = q + w.

17. Why does DU not depend on how the system gets from the initial to the final state?

18. Why are T, P, and V state functions, but not q and w?

19. How does enthalpy differ from the energy of a system? How are the two related mathematically?

20. Describe the difference between a constant pressure process and a constant volume process.

Section 8-3

21. What are important features of fuels?

22. Sketch figure 8-6 and describe it in your own words.

23. Why is DHrxn < 0 for an exothermic reaction and > 0 for an endothermic one?

24. What are the values for standard states for T, P and concentration? How is the standard state denoted?

25. Given: PV = nRT, where P is pressue in atm, V is volume in L, T is temp in K, n is the number of moles, and R is the ideal gas constant.

Follow the solution to example 8-4, then work practice problem 8-4.

26. Work problems 8-7 through 8-13 odd.

Section 8-4

27. Hess's Law is one of the most useful features of knowing DHrxn. It tells us that the the enthalpy changes (or heat of a reactions) is additive. In other words, if a reaction can be shown to be a combination of two or more reactions, then its DHrxn is simply the sum of the DHrxn for each of the separate reactions.

Write out this relationship mathmatically.

28. Write out Example 8-5 with the solution.

29. The rules for Hess's Law have been summarized for you on page 259. Write them in your own words.

30. Study at Example 8-6. Then work out Practice Problem 8-6.

31. Work problems 8-17, 8-19 and 8-23.

Section 8-5

32. When one mole of a compound is formed from its elements, then the value of DHrxn can be called the heat of formation or standard molar enthalpy of formation. How is the symbol for this written? What value is given to the elements in their natural state and why was it chosen?

33. How does heat of combustion differ from heat of formation?

34. Study Example 8-7. Then work out Practice Problem 8-7.

35. Look at Table 8-2 on page 263. Notice that most of the values for heats of formation are negative. What kind of information does the sign and size of the heat of formation give you?

36. Write down Equation 8-21. See how this is used to solve Example 8-8. You use it to work Practice Problem 8-8.

37. Why must you be careful to specifiy the state of matter for each substance in the equation?

38. Work problems 8-25, 8-27 and 8-29.

Section 8-6

39. Heat capacity is the heat required to raise the temperature of a sample of a substance by one degree C (or 1 K) If this occurs at constant pressure, then it is designated by cp.
1. Write the mathematical definitions of cp in terms of qp and DH.
2. Express this relationship in terms of qp.
3. What is the SI unit for heat capacity?

40. Look at Example 8-10, then work Practice problem 8-10.

41. Define molar heat capacity. What is its unit?

42. Look at Table 8-3. Calculate the heat capacity for one gram each of Al, Cu, Fe, Ag, and Sn and all three states of water. This amount is called the specific heat (S.H., though your text uses Csp). What is its unit?

43. Follow Example 8-11, then work Practice problem 8-11.

44. Relate S.H. to cp and qp.

45. What is the relationship between the amount of q lost from one sample that is gained by another sample? What is the resultant temperature for each sample?

46. Follow carefully Example 8-13, then work Practice Problem 8-13.

47. Work problems 8-37, 8-39 and 8-41.

Section 8-7

48. Sketch and describe the 3 different kinds of molecular motion.

49. What is the rule of Dulong and Petit? What was its original use?

50. Notice from #42, that the molar heat capacity of liquid water is about twice that of ice or steam. Why might this be important to us? Try to think of a specific example of this being put to a good use.

51. Work problems 8-65 and either 8-66, 8-67 or 8-68.

Section 8-8

52. What is a calorimeter and on what principle does it work? Make a sketch of a simple coffee cup calorimeter and describe how it works..

53. How does DHrxn relate to qp?

54. What is a bomb calorimeter and how does it differ from a simple calorimeter you described in #50?

55. Follow Example 8-15, then work out Practice problem 8-15.

56. Work problems 8-47 and 8-49.

 Send questions, comments or suggestions to Gwen Sibert, at the Roanoke Valley Governor's School gsibert@rvgs.k12.va.us Back to Notes Menu