Is the Reaction Endothermic or Exothermic? - Using Bond Energies
Click on the calculation
tab and see the calculation
set up for this reaction.
This extends the molecules
in a box approach done in
class.
You may type in the yellow
areas only or use the arrows.
Sinex 2003
Is the Reaction Endothermic or Exothermic? - Using Bond Energies
In the yellow areas, enter the bond, number of bonds either broken or formed, and the their bond energy.
bonds breaking bonds forming
# #
bond number of bonds bond energy* bond number of bonds bond energy*
N=-N 1 942 942 N-H 6 386 2316
H-H 3 432 1296 0
0 0
0 0
0 0
total energy 2238 total energy 2316
for bond breaking (absorbed) for bond forming (released)
#
atoms & type (single, double, triple) energy released is given a negative sign -2316
*Bond energies can be Energy difference (DH) = -78 Is energy released?
found in your textbook endothermic positive
or at the : Wired Chemist. exothermic negative Is the reaction endothermic or exothermic?
(This is an estimate of DH.)
See graphical displays below
scroll down! Sinex 2003
Just comparing totals: Using convention of negative sign for energy given off:
Which is larger? products if difference is negative - exothermic
exothermic if difference is positive - endothermic
3000
reactants 2238
endothermic
2500
reactants
2000 2238 products -2316 These graphs will
2000
Bond energy
products 2316 difference -78 respond to changes
1500
in the bond energy
1000 1000
calculator above!!!
Bond energy
500
0
0 reactants products difference
reactants products -1000
if reactants > products: endothermic -2000
exothermic
if products > reactants: exothermic
-3000
Sinex 2007