Bond enthalpies: Flashcards
What is average bond enthalpy?
= energy needed to break one mole of a specific bond in a molecule in the gaseous state
= scientists take an average value across the range of different molecules
What does the bond enthalpy of a specific bond depend on?
= depends on the molecule where we find the bond
Why do we use mean bond enthalpies?
= every single bond in a compound is different
Why are these values positive?
= energy is required to break bonds- breaking bonds is endothermic
Why is there different values for the same bond in differnt molecukes?
= the same bond in different environments have different enthalpy changes
Why are standard enthalpy changes of formation and combustion more accurate then mean bond energies?
= these are averaged values for several compounds
=
Bond length with bond enthalpy?
= as bond length increases, the amount of energy required to break the bond decreases as pair of electrons are further away from the positive nucleus
Why are experimental results lower than calculated results?
= practically, there will be significant heat loss
= and incomplete combustion- less energy is released
What are enthalpies of combustion like in homologous series?
= sucessive members of the homologous series there is a constant rise as the number of carbon atoms jncreases
