Click to Chat
1800-1023-196
+91-120-4616500
CART 0
Use Coupon: CART20 and get 20% off on all online Study Material
Welcome User
OR
LOGIN
Complete Your Registration (Step 2 of 2 )
Application of bond energies (i) Determination of enthalpies of reactions Suppose we want to determine the enthalpy of the reaction. If bond energies given for C ¾ C, C = C, C¾H, and H ¾ H are 347.3, 615.0, 416.2 and 435.1KJ mol-1 respectively. ΔH = ΔHC=C + ΔHH–H + 4ΔHC–H – (ΔHC–C + 6ΔHC–H) = (615.0 + 435.1) – (347.3 + 832.4) => –129.6 KJ (ii) Determination of enthalpies of formation of compounds Consider the formation of acetone. H O H | || | 3C(g) + 6H(g) + O(g) ———> H — C — C — C — H ΔH = ? | | H H ΔHf = [3ΔHH–H + 1/2 ΔH0–0 + 3ΔHC(s)—>C(g)] – [2ΔHC–C + 6ΔHC–H + ΔHC=O] by putting the value of different bond energies you can determine the ΔHf . (iii) Determination of resonance energy If a compound exhibits resonance, there is a considerable difference between the enthalpies of formation as calculated from bond energies and those determined experimentally. As an example we may consider the dissociation of benzene. C6H6 (g) ———> 6C(g) + 6H(g) Assuming that benzene ring consists of three single and three double bonds (Kekule’s structure) the calculated dissociation energy comes out to be 5384.1 KJ from bond energies data. ΔHd = 3ΔHC–C + 3ΔHC=C + 6ΔHC–H The experimental value is known to be 5535.1 KJ/mol. Evidently, the energy required for the dissociation of benzene is 151 KJ more that the calculated value. The difference of 151 KJ gives the resonance energy of benzene. Exercise: Calculate the enthapy of combustion of benzene (l) on the basis of the following. (i) Resonance energy of benzene (l) = – 152 kJ mole–1 (ii) Enthalpy of hydrogenation of cyclohexene (l) = – 119 kJ mole–1 (iii) (ΔHf0)C6H12 = – 156 kJ mole–1 (iv) (ΔH0f)H2O = – 285.8 kJ mole–1 (v) (ΔHf0)CO2 = – 393.5 kJ mole–1 To read more, Buy study materials of Thermodynamics comprising study notes, revision notes, video lectures, previous year solved questions etc. Also browse for more study materials on Chemistry here.
(i) Determination of enthalpies of reactions
Suppose we want to determine the enthalpy of the reaction.
If bond energies given for C ¾ C, C = C, C¾H, and H ¾ H are 347.3, 615.0, 416.2 and 435.1KJ mol-1 respectively.
ΔH = ΔHC=C + ΔHH–H + 4ΔHC–H – (ΔHC–C + 6ΔHC–H)
= (615.0 + 435.1) – (347.3 + 832.4) => –129.6 KJ
(ii) Determination of enthalpies of formation of compounds
Consider the formation of acetone.
H O H
| || |
| |
ΔHf = [3ΔHH–H + 1/2 ΔH0–0 + 3ΔHC(s)—>C(g)] – [2ΔHC–C + 6ΔHC–H + ΔHC=O]
by putting the value of different bond energies you can determine the ΔHf .
(iii) Determination of resonance energy
If a compound exhibits resonance, there is a considerable difference between the enthalpies of formation as calculated from bond energies and those determined experimentally. As an example we may consider the dissociation of benzene.
C6H6 (g) ———> 6C(g) + 6H(g)
Assuming that benzene ring consists of three single and three double bonds (Kekule’s structure) the calculated dissociation energy comes out to be 5384.1 KJ from bond energies data.
ΔHd = 3ΔHC–C + 3ΔHC=C + 6ΔHC–H
The experimental value is known to be 5535.1 KJ/mol. Evidently, the energy required for the dissociation of benzene is 151 KJ more that the calculated value. The difference of 151 KJ gives the resonance energy of benzene.
Exercise:
Calculate the enthapy of combustion of benzene (l) on the basis of the following.
(i) Resonance energy of benzene (l) = – 152 kJ mole–1
(ii) Enthalpy of hydrogenation of cyclohexene (l) = – 119 kJ mole–1
(iii) (ΔHf0)C6H12 = – 156 kJ mole–1
(iv) (ΔH0f)H2O = – 285.8 kJ mole–1
(v) (ΔHf0)CO2 = – 393.5 kJ mole–1
To read more, Buy study materials of Thermodynamics comprising study notes, revision notes, video lectures, previous year solved questions etc. Also browse for more study materials on Chemistry here.
Signing up with Facebook allows you to connect with friends and classmates already using askIItians. It’s an easier way as well. “Relax, we won’t flood your facebook news feed!”
Post Question
Dear , Preparing for entrance exams? Register yourself for the free demo class from askiitians.
THIRD LAW OF THERMODYNAMICS:- In all heat engines,...
Enthalpy of Reaction It is the enthalpy change...
Enthalpy of a System The quantity U + PV is known...
Specific Heat Capacity or Specific Heat [c] Table...
Thermodynamic Change or Thermodynamic Process...
HESS’S LAW This law states that the amount...
Level 2 Objective Problems of Thermodynamics Level...
Work Done During Isothermal Expansion Table of...
Introduction to Thermodynamics Table of Content...
Application of Hess's Law 1. Calculation of...
The First Law of Thermodynamics:- The first law of...
Objective Questions of Thermodynamics and Answers...
Work Done During Adiabatic Expansion Table of...
Macroscopic Properties He properties associated...
Solved Problems on Specific Heat, Latent Heat and...
Solved Problems on Thermodynamics:- Problem 1:- A...
Thermodynamic State of a System and Macroscopic...
Second Law of Thermodynamics Table of Content...
Specific Heat Capacity and Its Relation with...
Miscellaneous Exercises Thermal Physics:- Problem:...
Gibbs Free Energy This is another thermodynamic...
Reversible and Irreversible Process:- Reversible...
BOMB CALORIMETER The bomb calorimeter used for...
Relationship between free Energy and Equilibrium...
Solved Examples on Thermodynamics:- Problem 1 :- A...
