Question

Bond Energy

Using the table calculate the overall energy change for this reaction.
1. How much energy is needed for bond breaking?
2. How much energy is needed for bond making?
3. What is the overall energy change? (overall energy change = reactants - products)#
4. Can you create an energy level diagram to represent this reaction?
H H
H-CEC-H
- H-C-C-H
11
+
2H-H
HH
Prom the table of the values of bond enthalpy, the values we need are:
Bond
Enthalpy (kJ/mol
H-H
432
Сас
239
CH
413
c-c
347

Answer 1

The required energy to break a C=0 bond is 749kj/mol and the energy to break an H-O bond is 428kj/mol, so in order to form those bonds we have to add a - for each of those values.

For bond making It takes roughly 100 kcal of energy to break 1 mol of C–H bonds, so we speak of the bond energy of a C–H bond as being about 100 kcal/mol.