9. using bond energies, estimate the change in Hr for the following reaction.
2NO + O2--->2NO2
A 1624 kJ
B -247kJ
C 661 kJ
D 54kJ
10. using bond energies estimate the change Hr for the follwing reaction
C + 1/2O2 +1/2 N--->O=C=N
a -611kJ
b 109kJ
c 2770kJ
d -1090 kJ
Don't you have a table in your text that lists bond energies? If you don't know where it is in the text, look in the index under energy, and then bond under that. There usually is a table for single bonds and another for multiple bonds. Look up the bond energies, then perform the following calculation:
Hrxn=(sum of B.E. for products) - (sum of B.E. for reactants).
If there is a coefficient, as in #1, multiply the B.E. by the coefficient as part of the sum above.
Post your work if you get stuck and need more assistance. Be sure to explain what you don't understand.
I made an error.
Hrxn = (sum of B.E. for reactants) - (sum B. E. for products).
To estimate the change in enthalpy (ΔHr) using bond energies, you need to first determine the bond energies for the bonds involved in the reaction. Bond energies represent the energy required to break one mole of a specific bond.
For question 9, the reaction is:
2NO + O2 ---> 2NO2
To calculate ΔHr, you need to know the bond energies for the bonds in NO, O2, and NO2.
The bond energies can be found in a table, usually in the section of the textbook that discusses energy, specifically under the subsection for bond energies. Look for tables that list bond energies for single bonds and multiple bonds.
Once you find the bond energies, you will calculate ΔHr using the equation:
ΔHr = (sum of bond energies for reactants) - (sum of bond energies for products)
For question 9, the bond energies you need are:
- Bond energy for N-O bond in NO
- Bond energy for O=O bond in O2
- Bond energy for N=O bond in NO2
- Bond energy for O=O bond in NO2
Sum up the bond energies for the reactants and subtract the sum of the bond energies for the products. The resulting value will be the estimated change in enthalpy (ΔHr) for the reaction.
For question 10, the same process applies. Look up the bond energies for the bonds involved in the reaction and perform the calculation:
ΔHr = (sum of bond energies for reactants) - (sum of bond energies for products)
Remember to consider the coefficients in the balanced equation when multiplying the bond energies.