Bond Enthalpies Flashcards
Bond enthalpies
Energy required to break 1 mole of a specified type of bond in a gaseous molecule
Endothermic, +ve value
Limitations of bond enthalpies
Actual bond enthlapy depends on chemical environment of bond
Average bond enthalpy calculated from actual bond enthalpies, no 1 true value
Not all enthalpy changes occur under standard conditions
Calculating enthalpy change from average bond enthalpy
Total bond enthalpy of reactants-total bond enthalpy of products=enthalpy change
Hess’ law
If a reaction can take place by 2 routes and the starting and finishing conditions are the same, total enthalpy change is the same
Hess cycle for the enthalpy change for delta f H
Reactants =>Products
^. ^
Elements
Hess cycle for the enthalpy change of delta c H
Reactant => Products
Combustion products
