Energetics Flashcards
Enthalpy change
Is only covalent
The heat energy measured under standard pressure
Standard enthalpy change
The heat energy change measured under standard conditions and a stated temp
Mean bond enthalpy
The energy needed to break down a particular covalent bond averaged over a range of molecules
What does a negative bond energy mean
It is exothermic
What does a positive bond energy mean
Endothermic
Units for bond energy
kj per mol
Why are endothermic bond energies positive
More energy is needed to break bonds so heat is taken in
Why are exothermic bond energies negative
Energy is released to form bonds so heat is released
Bond enthalpy
Energy needed to break a bond
Standard enthalpy change of formation
Enthalpy change when 1 mole of a compound is formed
from its elements in their standard state under standard conditions
Standard enthalpy change of combustion
Enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions with all reactants and products in their standard state
Standard enthalpy change of reaction
Enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation under standard conditions with all reactants and products in their standard state
Hess’s law
Total enthalpy change for a reaction is independent from the route taken
Hesss law arrow rule
Against the arrow is minus
With the arrow is positive
What do you do to the bond energies in hesss law
Times them to the molar quantities
