IB Chemistry Energetics

Which enthalpy change cannot be calculated directly from average bond enthalpy data?

Average bond enthalpies give data for species in the gaseous phase (so cannot be caculated when not gaseous)

Comment on the average bond enthalpies of the reactants vs the products

The products have a higher total average bond enthalpy than the reactants. The products are at a lower energy level than the reactants meaning that the total average bond enthalpy of formation of bonds in the products is greater than the total average bond enthalpy of breaking of bonds in the reactants.

Define average bond enthalpy

The energy required to break one mole of covalent bonds in the gaseous state under standard conditions to give gaseous atoms
averaged over a range of similar compounds

Define enthalpy change of formation

Enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions.

Define standard bond enthalpy

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