Thermodynamics Review

1. Thermodynamics Review

2. For #1-5, match the correct definition to the vocabulary term. 1. Law of Conservation of Energy 4. Calorie 2. Temperature 5. Heat 3. Enthalpy (a) Measure of random motions of the components of a substance (b) flow of energy due to a temperature difference (c) amount of energy required to raise the temperature of one gram of water by one Celsius degree. (d) Measure of the change in heat flow from a chemical reaction (e) Energy is neither created nor destroyed

3. Answers: • 1) e • 2) a • 3) d • 4) c • 5) b

4. 6) What term describes when heat flow stops?

5. Answer • 6) thermal equilibrium

6. 7) Distinguish between what a positive sign on ΔH and a negative sign on ΔH would indicate.

7. Answer • 7) Positive= endothermic Negative= exothermic

8. 8) Calculate the energy needed to vaporize 3.88 moles of water.

9. Answer • 8) 158,000 J 1.58 x 105 J 158 kJ

10. 9) Determine the mass of water needed for 835 J of energy to raise its temperature from 25oC to 76oC.

11. Answer • 9) 3.9 g

12. 10) Would the dotted lines get shorter or longer upon condensing the water?

13. ANSWER • Shorter

14. 11) Is deposition endothermic or exothermic?

15. Answer • 11) Exothermic

16. 12) Iron III oxide and carbon react to produce iron and carbon dioxide. The temperature decreases by 10oC. Was it endothermic or exothermic?

17. ANSWER • Endothermic (chemical reaction got colder)

18. 13) Is sublimation endothermic or exothermic?

19. Answer • 13) Endothermic

20. 14) How many calories is 28.4 Joules?

21. Answer • 14) 6.79 cal

22. 15) Calculate the total energy required to melt 15.0 grams of ice.

23. Answer • 15) 5,010 J

24. 16) Distinguish an intermolecular force from an intramolecular force in a diagram.

25. Answer intramolecular force intermolecular force

26. 17) Which type of force is broken during vaporization, intermolecular or intramolecular?

27. ANSWER • Intermolecular (phase changes are physical, not chemical- no bonds break)

28. 18) Two reactants at 25oC are mixed in a container and the new temperature reads 32oC. Was the reaction endothermic or exothermic?

29. ANSWER • Exothermic (chemical reaction got hotter)

30. 19) 200. grams of water at 30.0oC are mixed with 20.0 grams of silver at 350oC. Find the final temperature of the system. • Cp of silver is 0.235 J/goC.

31. Answer • 19) 32oC

32. 20) Is melting endothermic or exothermic?

33. Answer • 20) Endothermic

34. 21) Where on the curve is there a mix of liquid and vapor?

35. Answer • segment DE

36. 22) At which point is there no more solid remaining?

37. Answer • 22) C

38. 23) In what part of the curve would the substance have a definite volume, but no definite shape?

39. Answer • 23) Line CD

40. 24) At plateau BC, two difference processes are occurring. Which ones?

41. Answer • 24) Melting and Freezing

42. 25) In what part of the curve would the molecules have the lowest kinetic energy?

43. Answer • 25) A

44. 26) How much heat is required to warm 15.0 g of water from 0 degrees Celsius to 100 degrees Celsius?

45. Answer • 26) 6,000 J

46. 27) A 135 g sample of aluminum at 400. degrees Celsius is placed in water at 25 degrees Celsius. The final temperature of the system is 80 degrees Celsius. Find the mass of the water used. • Cp aluminum = 0.89 J/goC

47. Answer • 27) 200 g

48. 28) What is fusion?

49. Answer • 28) Melting/Freezing

50. 29) Does the graph below represent an endothermic or an exothermic reaction?