enthalpy changes Flashcards
use ideas about the enthalpy changes that take place during bond breaking and bond making to explain why some reactions are exothermic
bond breaking is endothermic and bond forming is exothermic
less energy is released when bonds are broken than when bonds are formed
suggest two reasons why standard enthalpy changes of combustion determined experimentally are less exothermic than the calculated theoretic values
incomplete combustion
non-standard conditions
heat lost to surroundings
suggest why the enthalpy change of formation cannot be determined directly
other products may be produced
explain the bonding in a C=C double bond
use the orbital overlap model
C=C bonds are formed by the sideways overlap of P orbitals from 2 carbon atoms
pi bond is formed above and below plane of molecule
suggest why the average bond enthalpy of a C=C bond is not twice the bond enthalpy of a C-C bond
C=C bonds contain one sigma bond and a pi bond
pi bonds weaker than sigma bonds
define average bond enthalpy
average bond enthalpy when one mole of gaseous covalent bonds are broken