What's the difference between average bond enthalpy and exact bond enthalpy?

Average bond enthalpy is the mean energy needed to break a type of bond, while exact bond enthalpy is specific to a particular molecule.

Average bond enthalpy is a measure of the energy required to break a specific type of bond in one mole of gaseous molecules, averaged over similar compounds. It is a useful concept in chemistry because it allows us to make general predictions about the energy changes involved in chemical reactions. However, it is an average value and does not take into account the specific environment in which a bond exists. For example, the average bond enthalpy for a C-H bond is around 413 kJ/mol, but this value can vary depending on the specific molecule in which the bond is found.

On the other hand, exact bond enthalpy refers to the energy required to break a specific bond in a particular molecule. It is a more precise measure than average bond enthalpy because it takes into account the unique environment of the bond, including the specific atoms involved and their arrangement in the molecule. For instance, the exact bond enthalpy for a C-H bond in methane (CH4) might be different from that in ethane (C2H6), even though both are C-H bonds.

In summary, while average bond enthalpy provides a general idea of the energy required to break a type of bond, exact bond enthalpy gives a more precise measure for a specific bond in a particular molecule. Both concepts are important in understanding the energy changes involved in chemical reactions, but they offer different levels of precision and detail. Understanding the difference between these two concepts can help you better understand and predict the behaviour of different chemical reactions.