5.3 Bond Enthalpies Flashcards
What is the average bond enthalpy (bond energy)?
The energy required to break one mole of covalent bonds in a gaseous molecule under standard conditions. The value quoted is the average amount of energy to break a particular bond in a range of similar molecules.
Why is the enthalpy change for endothermic reactions positive?
Because bond breaking requires energy.
Why is the enthalpy change for exothermic reactions negative?
Because bond making releases energy.
Why do bond energies only apply to reactions in the gaseous state?
The enthalpy change for the reaction could not be worked out using bond enthalpies excuse water is in the liquid states and intermolecular forces must be taken into account.
When will a reaction in the gas phase be exothermic?
If more energy is realised when bonds are formed than is required to break bonds. This could be the case if stronger/ more bonds are made than are broken.
