Bond Enthalpies - AP Chemistry
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What is the bond enthalpy of a C-H bond in kJ/mol?
What is the bond enthalpy of a C-H bond in kJ/mol?
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Approximately 413 kJ/mol. Common value for single C-H bonds in organic molecules.
Approximately 413 kJ/mol. Common value for single C-H bonds in organic molecules.
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What is the bond enthalpy of a C=O bond in carbon dioxide?
What is the bond enthalpy of a C=O bond in carbon dioxide?
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799 kJ/mol. Strong double bond in carbon dioxide molecule.
799 kJ/mol. Strong double bond in carbon dioxide molecule.
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What is the bond enthalpy of an N-H bond?
What is the bond enthalpy of an N-H bond?
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391 kJ/mol. Standard value for nitrogen-hydrogen single bonds.
391 kJ/mol. Standard value for nitrogen-hydrogen single bonds.
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What is the bond enthalpy of an F-F bond?
What is the bond enthalpy of an F-F bond?
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157 kJ/mol. Weak bond due to lone pair repulsion between fluorines.
157 kJ/mol. Weak bond due to lone pair repulsion between fluorines.
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Which bond typically has a higher bond enthalpy: C=C or C-C?
Which bond typically has a higher bond enthalpy: C=C or C-C?
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C=C. Double bonds are stronger than single bonds.
C=C. Double bonds are stronger than single bonds.
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What is the definition of bond enthalpy?
What is the definition of bond enthalpy?
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The energy required to break one mole of a bond in gaseous molecules. Always measured for gaseous species at standard conditions.
The energy required to break one mole of a bond in gaseous molecules. Always measured for gaseous species at standard conditions.
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What is the bond enthalpy of an O=O bond?
What is the bond enthalpy of an O=O bond?
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498 kJ/mol. Strong double bond between oxygen atoms in $O_2$.
498 kJ/mol. Strong double bond between oxygen atoms in $O_2$.
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Compare bond enthalpies: O-H vs C-H.
Compare bond enthalpies: O-H vs C-H.
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O-H > C-H. O-H bond (463) is stronger than C-H bond (413).
O-H > C-H. O-H bond (463) is stronger than C-H bond (413).
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Identify the bond with the highest bond enthalpy: C-H, N≡N, O=O.
Identify the bond with the highest bond enthalpy: C-H, N≡N, O=O.
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N≡N. N≡N has the highest enthalpy due to triple bonding.
N≡N. N≡N has the highest enthalpy due to triple bonding.
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What happens to bond enthalpy as bond length increases?
What happens to bond enthalpy as bond length increases?
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Bond enthalpy decreases. Longer bonds have weaker attractive forces between atoms.
Bond enthalpy decreases. Longer bonds have weaker attractive forces between atoms.
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What is the bond enthalpy of a C=O bond in carbon dioxide?
What is the bond enthalpy of a C=O bond in carbon dioxide?
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799 kJ/mol. Strong double bond in carbon dioxide molecule.
799 kJ/mol. Strong double bond in carbon dioxide molecule.
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What is the bond enthalpy of an N-H bond?
What is the bond enthalpy of an N-H bond?
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391 kJ/mol. Standard value for nitrogen-hydrogen single bonds.
391 kJ/mol. Standard value for nitrogen-hydrogen single bonds.
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What does a negative enthalpy change indicate about a reaction?
What does a negative enthalpy change indicate about a reaction?
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The reaction is exothermic. Energy is released to the surroundings during reaction.
The reaction is exothermic. Energy is released to the surroundings during reaction.
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Calculate the bond enthalpy change for breaking 2 Cl-Cl and forming 2 Cl-H. Use 242 and 431 kJ/mol.
Calculate the bond enthalpy change for breaking 2 Cl-Cl and forming 2 Cl-H. Use 242 and 431 kJ/mol.
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$\Delta H = 2(242) - 2(431) = -378 \text{ kJ/mol}$. Breaking uses 484 kJ/mol, forming releases 862 kJ/mol.
$\Delta H = 2(242) - 2(431) = -378 \text{ kJ/mol}$. Breaking uses 484 kJ/mol, forming releases 862 kJ/mol.
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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).
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).
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$\Delta H = 2(436) - 2(463) = -54 \text{ kJ/mol}$. Breaking requires 872 kJ/mol, forming releases 926 kJ/mol.
$\Delta H = 2(436) - 2(463) = -54 \text{ kJ/mol}$. Breaking requires 872 kJ/mol, forming releases 926 kJ/mol.
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What is the bond enthalpy of an O-H bond?
What is the bond enthalpy of an O-H bond?
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463 kJ/mol. Standard value for oxygen-hydrogen bonds in water.
463 kJ/mol. Standard value for oxygen-hydrogen bonds in water.
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Calculate the enthalpy change: breaking H-H and Cl-Cl, forming 2 H-Cl. Use 436, 242, and 431 kJ/mol.
Calculate the enthalpy change: breaking H-H and Cl-Cl, forming 2 H-Cl. Use 436, 242, and 431 kJ/mol.
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$\Delta H = (436 + 242) - 2(431) = -184 \text{ kJ/mol}$. Breaking uses 678 kJ/mol, forming releases 862 kJ/mol.
$\Delta H = (436 + 242) - 2(431) = -184 \text{ kJ/mol}$. Breaking uses 678 kJ/mol, forming releases 862 kJ/mol.
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What is the bond enthalpy of a N=N bond?
What is the bond enthalpy of a N=N bond?
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418 kJ/mol. Standard value for nitrogen-nitrogen double bonds.
418 kJ/mol. Standard value for nitrogen-nitrogen double bonds.
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How does bond strength relate to bond enthalpy?
How does bond strength relate to bond enthalpy?
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Stronger bonds have higher bond enthalpies. Higher enthalpy means more energy needed to break the bond.
Stronger bonds have higher bond enthalpies. Higher enthalpy means more energy needed to break the bond.
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Calculate the bond enthalpy change for breaking 1 O=O and forming 2 O-H bonds. Use 498 and 463 kJ/mol.
Calculate the bond enthalpy change for breaking 1 O=O and forming 2 O-H bonds. Use 498 and 463 kJ/mol.
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$\Delta H = 498 - 2(463) = -428 \text{ kJ/mol}$. Breaking uses 498 kJ/mol, forming releases 926 kJ/mol.
$\Delta H = 498 - 2(463) = -428 \text{ kJ/mol}$. Breaking uses 498 kJ/mol, forming releases 926 kJ/mol.
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Which bond is generally stronger, N≡N or N=N?
Which bond is generally stronger, N≡N or N=N?
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N≡N. Triple bonds have higher bond enthalpies than double bonds.
N≡N. Triple bonds have higher bond enthalpies than double bonds.
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Identify whether a reaction is endothermic or exothermic when $\Delta H$ is positive.
Identify whether a reaction is endothermic or exothermic when $\Delta H$ is positive.
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Endothermic. Positive $\Delta H$ means energy is absorbed from surroundings.
Endothermic. Positive $\Delta H$ means energy is absorbed from surroundings.
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State whether forming a bond is endothermic or exothermic.
State whether forming a bond is endothermic or exothermic.
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Exothermic. Energy is released when atoms come together to form bonds.
Exothermic. Energy is released when atoms come together to form bonds.
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What type of reaction is indicated if the total bond enthalpies of products are greater than reactants?
What type of reaction is indicated if the total bond enthalpies of products are greater than reactants?
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Endothermic reaction. More energy required to break bonds than released forming them.
Endothermic reaction. More energy required to break bonds than released forming them.
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What is the bond enthalpy of a C-H bond in kJ/mol?
What is the bond enthalpy of a C-H bond in kJ/mol?
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Approximately 413 kJ/mol. Common value for single C-H bonds in organic molecules.
Approximately 413 kJ/mol. Common value for single C-H bonds in organic molecules.
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Calculate the bond enthalpy change for breaking N≡N and forming 2 N-H bonds. Use 941 and 391 kJ/mol.
Calculate the bond enthalpy change for breaking N≡N and forming 2 N-H bonds. Use 941 and 391 kJ/mol.
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$\Delta H = 941 - 2(391) = 159 \text{ kJ/mol}$. Breaking uses 941 kJ/mol, forming releases 782 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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What factor primarily affects the bond enthalpy?
What factor primarily affects the bond enthalpy?
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Bond strength. Bond enthalpy reflects the energy needed to break bonds.
Bond strength. Bond enthalpy reflects the energy needed to break bonds.
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What is the bond enthalpy of an O=O bond?
What is the bond enthalpy of an O=O bond?
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498 kJ/mol. Strong double bond between oxygen atoms in $O_2$.
498 kJ/mol. Strong double bond between oxygen atoms in $O_2$.
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Which bond typically has a higher bond enthalpy: C=C or C-C?
Which bond typically has a higher bond enthalpy: C=C or C-C?
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C=C. Double bonds are stronger than single bonds.
C=C. Double bonds are stronger than single bonds.
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What is the definition of bond enthalpy?
What is the definition of bond enthalpy?
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The energy required to break one mole of a bond in gaseous molecules. Always measured for gaseous species at standard conditions.
The energy required to break one mole of a bond in gaseous molecules. Always measured for gaseous species at standard conditions.
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