MUNISH KAKAR's INSTITUE OF CHEMISTRY
ENTHALPY CHANGE & HESS's LAW ( WS #4 )
Q1.
∆H and ∆E for the reaction, S(s) +
(a) ∆H = ∆E – 0.5 RT
Q2.
3
O2(g) → SO3(g) are related as:
2
(b) ∆H = ∆E – 1.5RT (c) ∆H = ∆E + RT
(d) ∆H = ∆E + 1.5 RT
The enthalpy of solution of BaCl2(s) and BaCl2.2H2O(s) are – 20.6 and 8.8 kJ mol-1
respectively. The enthalpy change for the reaction,BaCl2(s) + 2H2O  Bacl2.2H2O(s); is:
(a) 29.4 kJ
Q3.
(b) – 11.8 kJ
(c) – 20.6 kJ
(d) – 29.4 kJ
The heat of combustion of CH4(g), C(graphite) and H2(g) are 20 kcal, - 40 kcal and – 10
kcal respectively. The heat of formation of methane is:
(a) – 40 kcal
Q4.
(b) + 40 kcal
(c) – 80 kcal
(d) + 80 kcal
Under identical conditions, how many mL of each 1 M KOH and 0.5 M H 2SO4 solutions
are required to produce a resulting volume of 100 mL with the highest rise in
temperature?
(a) 75, 25
Q5.
(b) 25, 75
(c) 60, 40
(d) 50, 50
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
Q6.
Q7.
Q8.
Q9.
(b) T1 = 2T2
(c) T1 = 4T2
(d) T2 = 9T1
Identify the reaction in which the heat liberated corresponds to the heat of formation (∆H):
(a) C (diamond) + O2(g) → CO2(g) + heat
(b) 2H2(g) + O2(g) → 2H2O(g) + heat
(c) C (diamond) + 2H2(g) → CH4(g) + heat
(d) S (rhombic) + O2(g) → SO2(g) + heat
Which of the following is an endothermic reaction?
(a) 2H2(g) + O2(g) → 2H2O(l)
(b) N2(g) + O2(g) → 2NO(g)
(c) NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
(d) C2H5OH(aq) + 3O2(g) → 2CO2(g) + 3H2O(l)
Which of the following reactions is exothermic ?
(a) CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
(b) Fe(s) + S(s) → FeS(s)
(c) NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
(d) All of these
Which one of the following is not applicable for a thermochemical equation?
(a) It tells about physical state of reactants and products
(b) It tells whether the reaction is spontaneous
(c) It tells whether the reaction is exothermic or endothermic
(d) It tells about the allotropic form (if any) of the reactants
Q10. The enthalpies of all elements in their standard state at 25°C and one atmosphere
pressure are:
(a) same
(b) always positive
Q11. According to the equation,C6H6(l) +
(c) always negative
15
O2(g) → 6CO2(g) + 3H2O(l);
2
(d) zero
∆H = -3264.4 kJ mol-1
the energy evolved when 7.8 g benzene is burnt in air will be:
(a) 163.22 kJ
(b) 32.64 kJ
(c) 3.264 kJ
(d) 326.4 kJ
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MUNISH KAKAR's INSTITUE OF CHEMISTRY
Q12. The enthalpy change for the reaction,2C(graphite) + 3H2(g) → C2H6(g)is called:
(a) enthalpy of formation
(b) enthalpy of combustion
(c) enthalpy of hydrogenation
(d) enthalpy of vaporization
Q13. The heat of combustion of C(graphite) is -393.5 kJ mol-1. The heat of formation of CO2 from
graphite is ….. kJ mol-1:
(a) 393.5
(b) -393.5
(c) -787.0
(d) 787.0
Q14. The heat of neutralization of any strong acid and strong base is always constant and ∆H =
- 57.3 kJ. This is because:
(a) both the acid and base undergo complete ionization
(b) during neutralization, salt and water are formed
(c) 1 mole of water is formed from H+ and OH- ions
(d) the reaction is exothermic
Q15. The amount of heat liberated when one mole of NH4OH reacts with one mole of HCl is:
(a) 13.7 kcal (b) more than 13.7 kcal
(c) less than 13.67 kcal (d) cannot be predicted
Q16. Heat of neutralization for the reaction,NaOH + HCl → NaCl + H 2O is 57.1 kJ mol-1. The
heat released when 0.25 mole of NaOH is titrated against 0.25 mole of HCl will be ;
(a) 22.5 kJ
(b) 57.1 kJ
(c) 28.6 kJ
(d) 14.3 kJ
Q17. In which of the following neutralization reactions, the heat of neutralization will be
highest?
(a) HCl and NaOH (b) CH3COOH and NaOH (c) CH3COOH and NH4OH (d) HCl and NH4OH
Q18. “The enthalpy of formation of a compound is equal in magnitude but of opposite sign to
the enthalpy of decomposition of that compound under the same conditions.” This law
was presented by:
(a) Hess
(b) Le Chatelier
(c) Kirchhoff
(d) Lavoisier and Laplace
Q19. “The change of enthalpy of a chemical reaction is the same whether the reaction takes
place in one step or in several steps”. This law was presented by:
(a) Hess
(b) Le Chatelier
(c) van‟t Hoff
(d) Kirchhoff
Q20. 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
(c) +18.69 kJ
(d) -1.13 kJ
Q21. What will be the heat of formation of methane, if the heat of combustion of carbon is „-x‟
kJ, heat of formation of water is „-y‟ kJ and heat of combustion of methane is „-z‟ kJ?
(a) (-x – y + z) kJ
Q22. Given,
(b) (-z – x + 2y) kJ
(c) (-x – 2y – z) kJ
(d) (-x – 2y + z) kJ
C(s) + O2(g) → CO2(g) + 94.2 kcal
H2(g) + ½ O2(g) → H2O(l) + 68.3 kcal
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) + 210.8 kcal . H form (CH 4 ) is :
(a) 45.9
(b) 47.8
(c) 20.0
(d) 47.3
Q23. On combustion carbon forms two oxides CO and CO2, heat of formation of CO2 is -94.3
kcal and that of CO is -26.0 kcal. Heat of combustion of carbon is:
(a) -26.0 kcal
(b) -68.3 kcal
(c) -94.3 kcal
(d) -120.3 kcal
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MUNISH KAKAR's INSTITUE OF CHEMISTRY
Q24. Standard heat of formation for CCl4, H2O, CO2 and HCl at 298 K are -25.5, -57.8, -94.1
and -22.1 kJ/mol respectively. For the reaction,CCl4 + 2H2O → CO2 + 4HCl , what is ∆H ?
(a) 36.4 kJ
(b) 20.7 kJ
(c) -20.7 kJ
(d) -41.4 kJ
Q25. Heat of combustion of CH4, C2H6, C2H4 and C2H2 are -212.8, -373.0, -337.0 and -310.5
kcal respectively at the same temperature. The best fuel among these gases is:
(a) CH4
(b) C2H6
(c) C2H4
(d) C2H2
Q26. If enthalpies of formation for C2H4(g), CO2(g) and H2O(l) at 25°C and 1 atm pressure be 52,
-394 and -286 kJ mol-1 respectively, enthalpy of combustion of C2H4(g) will be:
(a) +141.2 kJ mol-1 (b) +1412 kJ mol-1 (c) -141.2 kJ mol-1 (d) -1412 kJ mol-1
Q27. S +
3
O2 → SO3 + 2x kcal;SO2 + ½ O2 → SO3 + y kcal . The heat of formation of SO2 is:
2
(a) y – 2x
(b) 2x + y
(c) x + y
(d) 2x/y
Q28. The heat of formation (∆H of ) of H2O(l) is equal to:
(a) zero
(b) molar heat of combustion of H2(l)
(c) molar heat of combustion of H2(g)
(d) sum of heat of formation of H2O(g) and O2(g)
Q29. The heat liberated when 1.89 g of benzoic acid is burnt in a bomb calorimeter at 25°C
increases the temperature of 18.94 kg of water by 0.632°C. If the specific heat of water at
25°C is 0.998 cal g-1 deg-1, the value of heat of combustion of benzoic acid is:
(a) 881.1 kcal
(b) 771.4 kcal
(c) 981.1 kcal
(d) 871.2 kcal
Q30. In an insulated container 2 mole of a liquid, molar volume 100 mL at 1 bar. Liquid is
steeply taken to 100 bar, when volume of liquid decreases by 1 mL. Find H and U for
the process.ANS :  E = 100 bar ml ,  H = 9900 bar ml
Q31. The reaction, NH2CN(s) +
3
O2(g)  N2(g) + CO2(g) + H2O(l); is carried out in a bomb
2
calorimeter and the heat liberated during the course of reaction was found to be -742.7 kJ
mol-1 at 25oC. Calculate the heat of reaction at constant pressure at 25oC.
 741.4 kJ
Q32. When 12.0 g of carbon reacted with oxygen to form CO and CO 2 at 25oC and constant
pressure, 75.0 kcal of heat was liberated and no carbon remained. Calculate the mass of
oxygen needed for it and the mole of CO and CO 2 formed. Given, Hf CO2 = -94.05 and Hf
CO = -26.41 kcal mol-1. mole of CO2 , CO are 0.72 &0.28, mass of O2 = 27.5 g
Q33. Calculate the lattice enthalpy of LiF; given that the enthalpy of
(i) Sublimation of lithium is 155.2 kJ/mole.
(ii) Dissociation of 1 mole of F2 at 75.3 kJ/mole.
(iii) Ionisation of lithium is 520 kJ/mole.
(iv) Electron gain enthalpy of 1 mole of F(g) is -333 kJ.
Ans :  973.8 kJ/mole
(v) Hf overall is -594.1 kJ/mole.
Q34. Calculate the lattice enthalpy of MgBr2 given that
Enthalpy of formation of MgBr2
=
- 524 kJ mol-1
Sublimation energy of Mg
=
148 kJ mol-1
Ionization energy of Mg
=
2187 kJ mol-1
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MUNISH KAKAR's INSTITUE OF CHEMISTRY
Vaporisation energy of Br2(l)
=
31 kJ mol-1
Dissociation energy of Br2(g)
=
193 kJ mol-1
Electron gain enthalpy of Br(g)
=
331 kJ mol-1
Ans :  2640 kJ/mole
Q35. Calculate the enthalpy of vaporization for water from the following:
H2(g) +
1
O2(g)  H2O(g);
2
H = -57.0 kcal
H2(g) +
1
O2(g)  H2O(l);
2
H = -68.3 kcal
Also calculate the heat required to change 1 g H2O(l) to H2O(g).
+ 11.3 kcal.
Q36. Calculate the heat of transition for carbon from the following:
Cdiamond + O2  CO2(g); H = -94.3 kcal
CAmorphous + O2  CO2(g);
H = -97.6 kcal
Also calculate the heat required to change 1 g of CDiamond to CAmorphous.
0.275kcal/g
Q37. An intimate mixture of Fe 2O3 and Al is used in solid fuel rocket. Calculate the fuel value
per g and per mL of mixture.
H Al2O 3 = 399.0 kcal,
H Fe2O3 = 199.0 kcal, density of Fe2O3 and Al are 5.2 g/mL and
2.7 g/mL respectively. Ans : 0.934 Kcal/g , 3.94 Kcal/ml
Q38. The heat of solution of anhydrous CuSO4 is -15.9 kcal and that of CuSO4, 5H2O is 2.8
kcal. Calculate the heat of hydration of CuSO4.
Ans :  18.7 Kcal
Q39. What would be heat released when:
(i) 0.25 mole of HCl in solution is neutralized by 0.25 mole of NaOH solution?
(ii) 0.5 mole of HNO3 in solution is mixed with 0.2 mole of KOH solution?
(iii) 200 cm3 of 0.2 M HCl is mixed with 300 cm3 of 0.1 M NaOH solution?
(iv) 400 cm3 of 0.2 M H2SO4 is mixed with 300 cm3 of 0.1 M NaOH solution?
Ans : (i) 14.27 kJ
(ii) 11.4 kJ
(iii) 1.713 kJ
(iv) 1.713 kJ
Q40. When 0.05 mole of HCl(aq) reacts with 0.05 mole of NaOH(aq) to form 0.05 mole of
NaCl(aq), 2.9 kJ of heat is produced. What is ΔH, the enthalpy change per mole of acid
reacting for the acid-base reaction under standard state ?
58 kJ/mole
Q41. Calculate the heat of neutralization from the following data. 200 ml. of 1 M HCl is mixed
with 400 ml. of 0.5 M NaOH. The temperature rise in calorimeter was found to be 4.4°C.
Water equivalent of calorimeter is 12 g and specific heat is 1 cal/ml/degree, for solution
Q42. 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.
Q43. 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.
 29.4 kJ/mole
Q44. 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.
+ 1.9 kJ1
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MUNISH KAKAR's INSTITUE OF CHEMISTRY
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