Bond Enthalpies - AP Chemistry

1. How does bond strength relate to bond enthalpy?

   Stronger bonds have higher bond enthalpies. Higher enthalpy means more energy needed to break the bond.

2. Identify the bond with the highest bond enthalpy: C-H, N≡N, O=O.

   N≡N. N≡N has the highest enthalpy due to triple bonding.

3. How does bond strength relate to bond enthalpy?

   Stronger bonds have higher bond enthalpies. Higher enthalpy means more energy needed to break the bond.

4. What is the bond enthalpy of an F-F bond?

   157 kJ/mol. Weak bond due to lone pair repulsion between fluorines.

5. Calculate the bond enthalpy change for breaking 2 Cl-Cl and forming 2 Cl-H. Use 242 and 431 kJ/mol.

   $\Delta H = 2(242) - 2(431) = -378 \text{ kJ/mol}$. Breaking uses 484 kJ/mol, forming releases 862 kJ/mol.

6. What is the bond enthalpy of a N=N bond?

   418 kJ/mol. Standard value for nitrogen-nitrogen double bonds.

7. What is the bond enthalpy of a H-Cl bond?

   431 kJ/mol. Standard value for hydrogen-chlorine bonds in HCl.

8. What type of reaction is indicated if the total bond enthalpies of products are greater than reactants?

   Endothermic reaction. More energy required to break bonds than released forming them.

9. What type of reaction is indicated if the total bond enthalpies of products are greater than reactants?

   Endothermic reaction. More energy required to break bonds than released forming them.

10. What happens to bond enthalpy as bond length increases?

    Bond enthalpy decreases. Longer bonds have weaker attractive forces between atoms.

11. What is the bond enthalpy of a C-H bond in kJ/mol?

    Approximately 413 kJ/mol. Common value for single C-H bonds in organic molecules.

12. What is the bond enthalpy of a C-O bond in methanol?

    358 kJ/mol. Standard value for carbon-oxygen single bonds.

13. State whether breaking a bond is endothermic or exothermic.

    Endothermic. Energy is required to overcome attractive forces between atoms.

14. Which bond typically has a higher bond enthalpy: C=C or C-C?

    C=C. Double bonds are stronger than single bonds.

15. What is the bond enthalpy of a C-H bond in kJ/mol?

    Approximately 413 kJ/mol. Common value for single C-H bonds in organic molecules.

16. Calculate the bond enthalpy change for breaking 1 O=O and forming 2 O-H bonds. Use 498 and 463 kJ/mol.

    $\Delta H = 498 - 2(463) = -428 \text{ kJ/mol}$. Breaking uses 498 kJ/mol, forming releases 926 kJ/mol.

17. What is the bond enthalpy of an O=O bond?

    498 kJ/mol. Strong double bond between oxygen atoms in $O_2$.

18. Calculate the enthalpy change: breaking H-H and Cl-Cl, forming 2 H-Cl. Use 436, 242, and 431 kJ/mol.

    $\Delta H = (436 + 242) - 2(431) = -184 \text{ kJ/mol}$. Breaking uses 678 kJ/mol, forming releases 862 kJ/mol.

19. What is the bond enthalpy of a C≡C bond?

    839 kJ/mol. Standard value for carbon-carbon triple bonds.

20. What is the bond enthalpy of an O=O bond?

    498 kJ/mol. Strong double bond between oxygen atoms in $O_2$.

21. What is the bond enthalpy of an F-F bond?

    157 kJ/mol. Weak bond due to lone pair repulsion between fluorines.

22. What is the bond enthalpy of a C=O bond in carbon dioxide?

    799 kJ/mol. Strong double bond in carbon dioxide molecule.

23. Calculate the bond enthalpy change for breaking N≡N and forming 2 N-H bonds. Use 941 and 391 kJ/mol.

    $\Delta H = 941 - 2(391) = 159 \text{ kJ/mol}$. Breaking uses 941 kJ/mol, forming releases 782 kJ/mol.

24. State whether forming a bond is endothermic or exothermic.

    Exothermic. Energy is released when atoms come together to form bonds.

25. Identify the bond with the highest bond enthalpy: C-H, N≡N, O=O.

    N≡N. N≡N has the highest enthalpy due to triple bonding.

26. Which bond is generally stronger, N≡N or N=N?

    N≡N. Triple bonds have higher bond enthalpies than double bonds.

27. State the formula for calculating the change in enthalpy using bond enthalpies.

    $\Delta H = \sum \text{(bond enthalpies of bonds broken)} - \sum \text{(bond enthalpies of bonds formed)}$. Energy in minus energy out gives the net enthalpy change.

28. What is the bond enthalpy of an O-H bond?

    463 kJ/mol. Standard value for oxygen-hydrogen bonds in water.

29. Identify the unit commonly used for bond enthalpy.

    Kilojoules per mole (kJ/mol). Standard unit for expressing energy per mole of substance.

30. What is the definition of bond enthalpy?

    The energy required to break one mole of a bond in gaseous molecules. Always measured for gaseous species at standard conditions.

31. What is the bond enthalpy of a N=N bond?

    418 kJ/mol. Standard value for nitrogen-nitrogen double bonds.

32. What is the definition of bond enthalpy?

    The energy required to break one mole of a bond in gaseous molecules. Always measured for gaseous species at standard conditions.

33. State whether forming a bond is endothermic or exothermic.

    Exothermic. Energy is released when atoms come together to form bonds.

34. Compare bond enthalpies: O-H vs C-H.

    O-H > C-H. O-H bond (463) is stronger than C-H bond (413).

35. State whether breaking a bond is endothermic or exothermic.

    Endothermic. Energy is required to overcome attractive forces between atoms.

36. State whether breaking a bond is endothermic or exothermic.

    Endothermic. Energy is required to overcome attractive forces between atoms.

37. What factor primarily affects the bond enthalpy?

    Bond strength. Bond enthalpy reflects the energy needed to break bonds.

38. What is the bond enthalpy of a C-C bond?

    348 kJ/mol. Standard value for single carbon-carbon bonds.

39. What is the bond enthalpy of an N-H bond?

    391 kJ/mol. Standard value for nitrogen-hydrogen single bonds.

40. Identify whether a reaction is endothermic or exothermic when $\Delta H$ is positive.

    Endothermic. Positive $\Delta H$ means energy is absorbed from surroundings.

41. What is the bond enthalpy of a C≡C bond?

    839 kJ/mol. Standard value for carbon-carbon triple bonds.

42. What is the bond enthalpy of a C-Cl bond?

    328 kJ/mol. Standard value for carbon-chlorine single bonds.

43. What is the bond enthalpy of a C=O bond in carbon dioxide?

    799 kJ/mol. Strong double bond in carbon dioxide molecule.

44. What factor primarily affects the bond enthalpy?

    Bond strength. Bond enthalpy reflects the energy needed to break bonds.

45. What is the bond enthalpy of an F-F bond?

    157 kJ/mol. Weak bond due to lone pair repulsion between fluorines.

46. Compare bond enthalpies: O-H vs C-H.

    O-H > C-H. O-H bond (463) is stronger than C-H bond (413).

47. Calculate the bond enthalpy change for breaking N≡N and forming 2 N-H bonds. Use 941 and 391 kJ/mol.

    $\Delta H = 941 - 2(391) = 159 \text{ kJ/mol}$. Breaking uses 941 kJ/mol, forming releases 782 kJ/mol.

48. What is the bond enthalpy of a C-N bond?

    305 kJ/mol. Standard value for carbon-nitrogen single bonds.

49. Which has a higher bond enthalpy: a single bond or a triple bond?

    A triple bond. More bonds mean stronger attraction and higher enthalpy.

50. What factor primarily affects the bond enthalpy?

    Bond strength. Bond enthalpy reflects the energy needed to break bonds.

51. What is the bond enthalpy of an N-H bond?

    391 kJ/mol. Standard value for nitrogen-hydrogen single bonds.

52. Which bond typically has a higher bond enthalpy: C=C or C-C?

    C=C. Double bonds are stronger than single bonds.

53. What is the bond enthalpy of an O=O bond?

    498 kJ/mol. Strong double bond between oxygen atoms in $O_2$.

54. What is the definition of bond enthalpy?

    The energy required to break one mole of a bond in gaseous molecules. Always measured for gaseous species at standard conditions.

55. Calculate the bond enthalpy change: breaking 2 H-H and forming 2 H-O. Use 436 kJ/mol (H-H) and 463 kJ/mol (H-O).

    $\Delta H = 2(436) - 2(463) = -54 \text{ kJ/mol}$. Breaking requires 872 kJ/mol, forming releases 926 kJ/mol.

56. Calculate the bond enthalpy change: breaking 1 C-C and forming 2 C-H. Use 348 and 413 kJ/mol.

    $\Delta H = 348 - 2(413) = -478 \text{ kJ/mol}$. Breaking uses 348 kJ/mol, forming releases 826 kJ/mol.

57. What is the bond enthalpy of a C-H bond in kJ/mol?

    Approximately 413 kJ/mol. Common value for single C-H bonds in organic molecules.

58. Calculate the bond enthalpy change for breaking 1 O=O and forming 2 O-H bonds. Use 498 and 463 kJ/mol.

    $\Delta H = 498 - 2(463) = -428 \text{ kJ/mol}$. Breaking uses 498 kJ/mol, forming releases 926 kJ/mol.

59. Calculate the bond enthalpy change for breaking 2 C=C and forming 3 C-C. Use 614 and 348 kJ/mol.

    $\Delta H = 2(614) - 3(348) = 240 \text{ kJ/mol}$. Breaking uses 1228 kJ/mol, forming releases 1044 kJ/mol.

60. Calculate the bond enthalpy change for breaking 1 O=O and forming 2 O-H bonds. Use 498 and 463 kJ/mol.

    $\Delta H = 498 - 2(463) = -428 \text{ kJ/mol}$. Breaking uses 498 kJ/mol, forming releases 926 kJ/mol.

61. What type of reaction is indicated if the total bond enthalpies of products are greater than reactants?

    Endothermic reaction. More energy required to break bonds than released forming them.

62. Which bond is generally stronger, N≡N or N=N?

    N≡N. Triple bonds have higher bond enthalpies than double bonds.

63. What is the bond enthalpy of a N=N bond?

    418 kJ/mol. Standard value for nitrogen-nitrogen double bonds.

64. State whether forming a bond is endothermic or exothermic.

    Exothermic. Energy is released when atoms come together to form bonds.

65. Compare bond enthalpies: O-H vs C-H.

    O-H > C-H. O-H bond (463) is stronger than C-H bond (413).

66. Identify whether a reaction is endothermic or exothermic when $\Delta H$ is positive.

    Endothermic. Positive $\Delta H$ means energy is absorbed from surroundings.

67. What is the bond enthalpy of an N-H bond?

    391 kJ/mol. Standard value for nitrogen-hydrogen single bonds.

68. Which bond is generally stronger, N≡N or N=N?

    N≡N. Triple bonds have higher bond enthalpies than double bonds.

69. How does bond strength relate to bond enthalpy?

    Stronger bonds have higher bond enthalpies. Higher enthalpy means more energy needed to break the bond.

70. What does a negative enthalpy change indicate about a reaction?

    The reaction is exothermic. Energy is released to the surroundings during reaction.

71. What happens to bond enthalpy as bond length increases?

    Bond enthalpy decreases. Longer bonds have weaker attractive forces between atoms.

72. Calculate the enthalpy change: breaking H-H and Cl-Cl, forming 2 H-Cl. Use 436, 242, and 431 kJ/mol.

    $\Delta H = (436 + 242) - 2(431) = -184 \text{ kJ/mol}$. Breaking uses 678 kJ/mol, forming releases 862 kJ/mol.

73. What happens to bond enthalpy as bond length increases?

    Bond enthalpy decreases. Longer bonds have weaker attractive forces between atoms.

74. What is the bond enthalpy of a C=O bond in carbon dioxide?

    799 kJ/mol. Strong double bond in carbon dioxide molecule.

75. Calculate the enthalpy change: breaking H-H and Cl-Cl, forming 2 H-Cl. Use 436, 242, and 431 kJ/mol.

    $\Delta H = (436 + 242) - 2(431) = -184 \text{ kJ/mol}$. Breaking uses 678 kJ/mol, forming releases 862 kJ/mol.

76. Identify the bond with the lowest bond enthalpy: H-H, Cl-Cl, F-F.

    F-F. Lone pair repulsion makes F-F weakest among halogens.

77. Identify whether a reaction is endothermic or exothermic when $\Delta H$ is positive.

    Endothermic. Positive $\Delta H$ means energy is absorbed from surroundings.

78. What is the bond enthalpy of a C-F bond?

    485 kJ/mol. Strong bond due to high electronegativity of fluorine.

79. What is the bond enthalpy of a C-F bond?

    485 kJ/mol. Strong bond due to high electronegativity of fluorine.

80. Which bond typically has a higher bond enthalpy: C=C or C-C?

    C=C. Double bonds are stronger than single bonds.

81. Calculate the bond enthalpy change for breaking N≡N and forming 2 N-H bonds. Use 941 and 391 kJ/mol.

    $\Delta H = 941 - 2(391) = 159 \text{ kJ/mol}$. Breaking uses 941 kJ/mol, forming releases 782 kJ/mol.

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