MUNISH KAKAR's INSTITUTE OF CHEMISTRY
BOND ENERGY & HEAT CAPACITY WS #5
Q1.
Calculate enthalpy change on freezing 1 mole of water at 100C to ice at  100C. Given that
Enthalpy
of
fusion
of
ice
at
0 0C
CP [ H 2O, l ]  75.3 J mol 1K 1 and CP [ H 2O, s]  36.8 J mol 1K 1.
Q2.
6.03
kJ/mole,
Ans :  7.15 kJ/mol
Calculate the amount of heat ( in kJ) required to raise temperature of 54g Al from 300K to
310 K. Given that Molar heat capacity of Al = 24 JK-1mol-1.
Q3.
is
Ans : 0.48 kJ
Calculate bond energy of O – O bond in H2O2. Given, ΔHf°(H2O2) = -136.3 kJ, B.E. of
O – H bond = 463.0 kJ mol-1, B.E. of H-H bond = 436 kJ mol-1, and B.E. of O = O bond =
495 kJ mol-1.
Ans.=+141.3 kJ mol-1
Q4.
Calculate bond energy of O-H bond. Given, ΔHf° (H2O(g)) = -241.82 kJ mol-1; B.E. of (H2) =
435.9 kJ mol-1; B.E. of O2 = 495.0 kJ mol-1.
Ans.=462.61 kJ mol-1
Q5.
The heat of combustion of ethyl alcohol (C2H5OH) is 1380.7 kJ mol-1.
If the heat of
formation of CO2 and H2O are 394.5 and 286.6 kJ mol-1 respectively, calculate the heat of
formation of ethyl alcohol.
Ans.=-268.1 kJ mol-1
Q6.
Heat of solution (ΔHsoln) for BaCl2.2H2O and BaCl2 are 8.8 and –20.6 kJ mol-1 respectively.
Calculate the heat of hydration of BaCl2 to BaCl2.2H2O.
Ans.=-29.4 kJ
Q7.
Calculate the heat change accompanying the transformation of C (graphite) to C
(diamond), given that the heats of combustion of graphite and diamond are 393.5 and
395.4 kJ mol-1 respectively.
Ans.=+1.9 kJ
Q8.
A 1.0 g magnesium atom in vapour phase absorbs 50.0 kJ energy to convert all Mg ions.
The energy absorbed is needed for the following changes:
Mg(g)  Mg+(g) + e;
H = 740 kJ mol-1
Mg+(g)  Mg2+ + e;
H = 1450 kJ mol-1
Find out the % of Mg+ and Mg2+ in final mixture. Ans : Mg+ = 69% , Mg2+ = 31%
Q9.
Calculate the CC bond energy from the following data:
(a) C(s)  C(g);
H = 170.9 kcal
(b)
1
H2  H(g);H = 52.1 kcal
2
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MUNISH KAKAR's INSTITUTE OF CHEMISTRY
(c) Heat of formation of ethane = -20.3 kcal
(d) CH bond energy = 99.0 kcal
Ans : 90.5 Kcal/mole
Q10. Using bond energy data, calculate heat of formation of isoprene.
5C(s) + 4H2(g) 
H2C  C  C  CH2
| |
CH3H
Given, CH = 98.8 kcal,
HH = 104 kcal,
CC = 83 kcal,
C(s)  C(g) = 171 kcal.
C=C = 147 kcal and
Ans : +20.6 kcal/mole
Q11. The dissociation energy of CH4 is 360 kcal/mol and of ethane is 620 kcal/mol. Calculate
CC bond energy.
Ans : 80 kcal/mole
Q12. Calculate enthalpy change of the following reaction:
H2C=CH2(g) + H2(g)  H3CCH3(g)
The bond energy of CH, CC, C=C and HH are 414, 347, 615 and 435 kJ mol-1
respectively.
Ans : -125 kJ/mole
Q13. Calculate the resonance energy of N2O from the following data in terms of bond energies :
N  N 946 kJ mol-1 N=N
418 kJ mol-1O=O
498 kJ mol-1N=O607 kJ mol-1
Given that H of of N2O is 82 kJ mol-1.
Ans : -88 kJ/mole
Q14. Estimate the average SF bond energy in SF6. The standard heat of formation values of
SF6(g), S(g) and F(g) are: -1100, 275 and 80 kJ mol-1 respectively.
Ans : 309.1 kJ/mole
Q15. A solution of 500 mL of 0.2 M KOH and 500 mL of 0.2 M HCl is mixed and stirred, the rise
in temperature is Ti. The experiment is repeated using 250 mL each of solution, the
temperature raised is T2. Which of the following is true ?
(a) T1 = T2
(b) T1 = 2T2
(c) T1 = 4T2
(d) T2 = 9T1
Q16. The resonance energy of N2O from the following data; Hf of N2O = 82 kJ mol-1. Bond
energies of N  N, N = N, O = O and N = O bonds are 946, 418 and 607 kJ mol -1
respectively is ;
(a) -88 kJ mol-1
(b) -170 kJ mol-1
(c) -82 kJ mol-1
(d) -258 kJ mol-1
Q17. The enthalpy of neutralization of oxalic acid ( H 2C2O4 )by a strong base is -25.4 kcal mol-1.
The enthalpy of neutralization of strong acid and strong base is -13.7 kcal eq-1. The
enthalpy of dissociation of oxalic acid is:
(a) 1 kcal mol-1
(b) 2 kcal mol-1
(c) 18.55 kcal mol-1 (d) 11.7 kcal mol-1
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Q18. The heat of combustion of yellow phosphorus and red phosphorus are -9.91 kJ and -8.78
kJ respectively. The heat of transition of yellow phosphorus to red phosphorus is:
(a) -18.69 kJ
(b) +1.13 kJ
Q19. If S + O2 → SO2;
(c) +18.69 kJ
(d) -1.13 kJ
∆H = -298.2 kJ
SO2 + ½ O2 → SO3;
∆H = -98.7 kJ
SO3 + H2O → H2SO4;
∆H = -130.2 kJ
H2 + ½ O2 → H2O;
∆H = -227.3 kJ
the heat of formation of H2SO4 will be:
(a) -754.4 kJ
(b) +320.5 kJ
(c) -650.3 kJ
(d) -433.7 kJ
Q20. The bond dissociation energies for Cl2, I2 and ICl are 242.3, 151 and 211.3 kJ/mol
respectively. The enthalpy of sublimation of iodine is 62.8 kJ/mol. What is the standard
enthalpy of formation of ICl(g)?
(a) -211.3 kJ/mol
(b) -14.6 kJ/mol
(c) 16.8 kJ/mol
(d) 33.5 kJ/mol
Q21. The bond dissociation energy of C-H in CH4 in C(g) + 4H(g) → CH4(g);
∆H = -397.8 kcal
is:
(a) +99.45 kcal
(b) -99.45 kcal
(c) +397.8 kcal
(d) +198.9 kcal
Q22. AB, A2 and B2 are diatomic molecules. If the bond enthalpies of A2, AB and B2 are in the
ratio 1:1:0.5 and the enthalpy of formation of AB from A2 and B2 is -100 kJ mol-1, what is
the bond enthalpy of A2?
(a) 400 kJ mol-1
(b) 200 kJ mol-1
(c) 100 kJ mol-1
(d) 300 kJ mol-1
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