Wize University Chemistry Textbook > Chemical Bonding

BDE Calculation

Bond Energies

Enthalpy (H) is the energy stored in bonds.

Bond dissociation energy (BDE) is the energy needed to break a chemical bond.

$\Delta H_{rxn}=\left[\left(\sum_{ }^{ }nH_{bonds\ broken}\right)-\left(\sum_{_{ }}^{ }nH_{bonds\ formed\ }\right)\right]$

Or (an easier way to think about it):

\boxed{\Delta Hrxn=[(\sum n BDE_{reactants})-[({\sum nBDE_{products})]}}

$\Delta H_{rxn}=$ enthalpy change for the reaction (kJ/mol)

BDE = bond energy per mole of bonds (kJ/mol), always positive

\boxed{\Delta Hrxn=[(\sum n BDE_{reactants})-[({\sum nBDE_{products})]}}

Photo by Rice University / CC BY

Practice: Bond Dissociation Energies

Predict the overall change in enthalpy (i.e. change in enthalpy, change in heat, ΔHrxn in kJ/mol) for the reaction:

N2 (g) + 3 H2 (g) → 2 NH3 (g)

BDE:

NN = 945 kJ/mol

H–H = 436 kJ/mol

N–H = 391 kJ/mol

I don't know

Extra Practice

Practice: Bond Energy

Calculate the BDE of N2 from the following reaction:

N2 (g) + 2H2 (g) → N2H4 (g); ∆Hr = +99 kJ / mol

H-H: BDE=436 kJ/mol

Chemical Bonding: Bond strength and energy

The following figure shows the potential energy diagrams for the carbon-carbon bond in ethane, ethene, and ethyne. Structures of these molecules are shown below. Identify which molecule corresponds to each potential energy curve.

Bond Energy

What is the total bond energy for the following molecule?

C - H 413 kJ/mol

C - C 347 kJ/mol

BDE Calculation

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Bond Energies

Practice: Bond Dissociation Energies

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Extra Practice