8.3.1 Mean Bond Enthalpies

• What is the definition of mean bond enthalpy?

  Average enthalpy change to break one mole of a bond in the gas phase
• Mean bond enthalpies are specific to the gas phase.
• Why are mean bond enthalpies less precise than individual bond enthalpies?

  They are average values
• Match the aspect with the correct type of bond enthalpy:

  Exact for a bond in a compound ↔️ Individual Bond Enthalpy

  Average across compounds ↔️ Mean Bond Enthalpy
• Mean bond enthalpies are applicable to all phases of matter.

  False
• Mean bond enthalpies are specific to the gas phase.
• What is one limitation of using mean bond enthalpies?

  They are not precise
• Mean bond enthalpies can be used to accurately calculate enthalpy changes in complex compounds.

  False
• What is the first step in calculating enthalpy changes using mean bond enthalpies?

  Identify all bonds broken and formed
• Calculate the enthalpy change for the reaction $H_{2}(g) +$$Cl_{2}(g) \rightarrow 2HCl(g)$ using mean bond enthalpies: H-H (436 kJ/mol), Cl-Cl (242 kJ/mol), H-Cl (431 kJ/mol).


  -184 kJ/mol
• What is the key characteristic of mean bond enthalpies regarding their values?

  They are average values
• Mean bond enthalpies are more precise than individual bond enthalpies.

  False
• What does mean bond enthalpy represent?

  Average bond energy
• Mean bond enthalpies are specific to the gas
• Mean bond enthalpies are useful for estimating reaction enthalpy changes.
• What is the formula to calculate reaction enthalpy using mean bond enthalpies?

  $\Delta H =$$\sum \text{bond enthalpies broken} - \sum \text{bond enthalpies formed}$
• Mean bond enthalpies are less precise
• Match the aspect with the correct type of bond enthalpy:

  Specificity ↔️ Exact for a bond in a compound

  Accuracy ↔️ High

  Applicability ↔️ Complex compounds
• Mean bond enthalpies are exact for a bond in a specific compound.

  False
• What is the definition of mean bond enthalpy?

  Average energy to break a bond
• Mean bond enthalpies are an average of bond energies.
• What are the limitations of mean bond enthalpies?

  Lower precision and gas phase restriction
• Steps to calculate enthalpy changes using mean bond enthalpies:

  1️⃣ Identify all bonds broken and formed

  2️⃣ Sum up bond enthalpies of bonds broken

  3️⃣ Sum up bond enthalpies of bonds formed

  4️⃣ Apply the formula

  5️⃣ Compare calculated value with experimental values
• What is the calculated enthalpy change for the reaction $H_{2}(g) +$$Cl_{2}(g) \rightarrow 2HCl(g)$ using mean bond enthalpies?


  -184 kJ/mol
• Mean bond enthalpies provide simple and quick enthalpy change estimations.
• Match the aspect with the correct type of bond enthalpy:

  Specificity ↔️ Exact value for a specific bond

  Applicability ↔️ Accurate analysis of bonds

  Dependence on environment ↔️ Highly affected
• What is bond dissociation enthalpy?

  Energy to break a specific bond
• The mean bond enthalpy of C-H bonds is used for estimating enthalpy changes in hydrocarbon reactions.
• What is the primary difference between mean bond enthalpy and bond dissociation enthalpy?

  Specificity
• Shorter bonds have higher bond enthalpies.
• How does electronegativity affect bond enthalpy?

  Greater difference increases it
• Mean bond enthalpy is specific to the gas phase.
• Mean bond enthalpy is an exact value for a specific bond.

  False
• What is the formula to calculate reaction enthalpy using mean bond enthalpies?

  $\Delta H =$$\sum \text{bond enthalpies broken} - \sum \text{bond enthalpies formed}$
• Mean bond enthalpy is the average enthalpy change when one mole of a particular bond is broken in the gas phase across various compounds.
• The formula to calculate reaction enthalpy using mean bond enthalpies is $\Delta H =$$\sum \text{bond enthalpies formed} - \sum \text{bond enthalpies broken}$.


  False
• Mean bond enthalpy represents an average of bond energies and is useful for estimating reaction enthalpy changes.
• What phase is mean bond enthalpy specific to?

  Gas phase
• Mean bond enthalpies are exact values for bond energies in specific compounds.

  False
• Mean bond enthalpies are used to approximate reaction enthalpies.