5.3a Average bond Enthalpy

Enthalpy-is the measurement of the energy in a thermodynamic system

Bond Enthalpy- is the energy required to break 1 mol of bonds in gaseous covalent molecules under standard conditions

Average bond enthalpy- the enthalpy change when (one mole of) the gaseous bond is broken (or formed);  average values obtained from a number of similar bonds;

You can use the average bond enthalpy (given in the data booklet section 11) to calculate the enthalpy of a specific reaction

• ∆H^θ > 0 : Endothermic (requires energy)​
• ∆H^θ < 0 : Exothermic (releases energy)​

• Bond forming releases energy and bond breaking requires energy

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Example: Find the enthalpy of formation for the chemical reaction below

​C₂H₄+HBr → C₂H₅Br

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​Don’t forget to use double bonds!