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JEE Solved Example on Thermodynamic 
JEE Mains 
Q1: Calculate the enthalpy of formation of ????
-
ions from the following thermochemical data: 
?? ?? ?? (?? )
? ?? (???? )
+
+ ????
-
(???? ) ; ?? ?? ?????? ?? °
= +???? . ???? ????
?? ?? ( ?? )
+
?? ?? ?? ?? (?? )
? ?? ?? ?? (?? )
; ?? ?? ?????? ?? °
= -?????? . ???? ????
 
(a) -?????? . ???? ???? 
(b) -?????? . ???? ???? 
(c) +?????? . ?? ???? 
(d) -?????? . ?? ???? 
Ans: (a) 
?H
°
= 57.32 = ? ?H
f
°
 (products ) - ? ?H
f
°
 (reactants )
57.32 = ?H
f
°
(OH
-
) + 285.83? H
f
°
(OH
-
) = -?????? . ???? ????
 
Q2: Using bond energy data, calculate heat of formation of isoprene  Given bond 
energy of C–H = 98.8 kcal, H–H = 104 kcal, C–C = 83 kcal, C=C = 147 kcal and ?H of C(s) ? C(g) = 171 
kcal 
(a) ???? . ?????????? ?????? -?? 
(b) ???? . ?????????? ?????? -?? 
(c) ?????????????? ?????? -?? 
(d) ?????????????? ?????? -?? 
Ans:  
?H = 5(171) + 4(104) - [(147 × 2) + (83 × 2) + (8 × 98.8)]
 = ???? . ?????????? 
 
 
 
 
 
 
Page 2


JEE Solved Example on Thermodynamic 
JEE Mains 
Q1: Calculate the enthalpy of formation of ????
-
ions from the following thermochemical data: 
?? ?? ?? (?? )
? ?? (???? )
+
+ ????
-
(???? ) ; ?? ?? ?????? ?? °
= +???? . ???? ????
?? ?? ( ?? )
+
?? ?? ?? ?? (?? )
? ?? ?? ?? (?? )
; ?? ?? ?????? ?? °
= -?????? . ???? ????
 
(a) -?????? . ???? ???? 
(b) -?????? . ???? ???? 
(c) +?????? . ?? ???? 
(d) -?????? . ?? ???? 
Ans: (a) 
?H
°
= 57.32 = ? ?H
f
°
 (products ) - ? ?H
f
°
 (reactants )
57.32 = ?H
f
°
(OH
-
) + 285.83? H
f
°
(OH
-
) = -?????? . ???? ????
 
Q2: Using bond energy data, calculate heat of formation of isoprene  Given bond 
energy of C–H = 98.8 kcal, H–H = 104 kcal, C–C = 83 kcal, C=C = 147 kcal and ?H of C(s) ? C(g) = 171 
kcal 
(a) ???? . ?????????? ?????? -?? 
(b) ???? . ?????????? ?????? -?? 
(c) ?????????????? ?????? -?? 
(d) ?????????????? ?????? -?? 
Ans:  
?H = 5(171) + 4(104) - [(147 × 2) + (83 × 2) + (8 × 98.8)]
 = ???? . ?????????? 
 
 
 
 
 
 
 
Q3: One mole of magnesium in the vapour state absorbed 1300 ???? of energy. If the first and 
second ionization energies of ???? are 750 and ???????? ???? ?????? -?? respectively, the final composition 
of the mixture is 
(a) ???? %????
+
and ???? %????
+?? 
(b) ???? %????
+
and ???? %????
+?? 
(c) ???? %????
+
and ???? %????
+?? 
(d) ???? %????
+
and ???? %????
+?? 
Ans: (c) 
Mg ? Mg
+
+ e
-
 
To ionise one mole of Mg completely 750 kJ is spent and energy left = 550 kJ. 
1450 kJ ionises 1 mole of Mg
+1
 
550 kJ ionises 0.38 mole of Mg
+1
 
Mg
+
? Mg
+2
+ e
-
1
1 - 0.38 0.38
% of Mg
+
= ???? % and that of Mg
+2
= ???? %
 
Q4:  
 
?????? + ?? ?? ? ???????? ; ?? ?? ?? = -?????? ?? … . . . (i) 
?????? + ?? ?? ? ???????? ; ?? ?? ?? = -?????? ?? ?? ?? + ?? . . . (ii) 
?? ?? ?? ? ?? ????
?? ( ?? ); ?? ?? ?? = -?????? ?? … . . (iii) 
 
?? ?? °
 for the following reaction ???????? + ?? ?? ?? ? ???????? + ?? ????
?? would be 
(a) +???????? ?? 
(b) -???????? ?? 
(c) +?????? ?? 
(d) -?????? ?? 
Ans: (d) 
?G
o
= 2? G
ZnO 
°
+ 2? G
SO
2
°
- 2? G
ZnS 
°
= [-616- 408] - [-293] = - 
731 J. 
Q5: The enthalpies of combustion of ?? (graphite) 
 and ?? (diamond) 
 are 393.5 and -?????? . ?? ???? /?????? 
respectively. The enthalpy of conversion of ?? (graphite) 
 to ?? (diamond) 
 in ???? /?????? is 
(a) -2.9 
(b) -888.9 
(c) 788.9 
(d) 1.9 
Ans: (d) 
Page 3


JEE Solved Example on Thermodynamic 
JEE Mains 
Q1: Calculate the enthalpy of formation of ????
-
ions from the following thermochemical data: 
?? ?? ?? (?? )
? ?? (???? )
+
+ ????
-
(???? ) ; ?? ?? ?????? ?? °
= +???? . ???? ????
?? ?? ( ?? )
+
?? ?? ?? ?? (?? )
? ?? ?? ?? (?? )
; ?? ?? ?????? ?? °
= -?????? . ???? ????
 
(a) -?????? . ???? ???? 
(b) -?????? . ???? ???? 
(c) +?????? . ?? ???? 
(d) -?????? . ?? ???? 
Ans: (a) 
?H
°
= 57.32 = ? ?H
f
°
 (products ) - ? ?H
f
°
 (reactants )
57.32 = ?H
f
°
(OH
-
) + 285.83? H
f
°
(OH
-
) = -?????? . ???? ????
 
Q2: Using bond energy data, calculate heat of formation of isoprene  Given bond 
energy of C–H = 98.8 kcal, H–H = 104 kcal, C–C = 83 kcal, C=C = 147 kcal and ?H of C(s) ? C(g) = 171 
kcal 
(a) ???? . ?????????? ?????? -?? 
(b) ???? . ?????????? ?????? -?? 
(c) ?????????????? ?????? -?? 
(d) ?????????????? ?????? -?? 
Ans:  
?H = 5(171) + 4(104) - [(147 × 2) + (83 × 2) + (8 × 98.8)]
 = ???? . ?????????? 
 
 
 
 
 
 
 
Q3: One mole of magnesium in the vapour state absorbed 1300 ???? of energy. If the first and 
second ionization energies of ???? are 750 and ???????? ???? ?????? -?? respectively, the final composition 
of the mixture is 
(a) ???? %????
+
and ???? %????
+?? 
(b) ???? %????
+
and ???? %????
+?? 
(c) ???? %????
+
and ???? %????
+?? 
(d) ???? %????
+
and ???? %????
+?? 
Ans: (c) 
Mg ? Mg
+
+ e
-
 
To ionise one mole of Mg completely 750 kJ is spent and energy left = 550 kJ. 
1450 kJ ionises 1 mole of Mg
+1
 
550 kJ ionises 0.38 mole of Mg
+1
 
Mg
+
? Mg
+2
+ e
-
1
1 - 0.38 0.38
% of Mg
+
= ???? % and that of Mg
+2
= ???? %
 
Q4:  
 
?????? + ?? ?? ? ???????? ; ?? ?? ?? = -?????? ?? … . . . (i) 
?????? + ?? ?? ? ???????? ; ?? ?? ?? = -?????? ?? ?? ?? + ?? . . . (ii) 
?? ?? ?? ? ?? ????
?? ( ?? ); ?? ?? ?? = -?????? ?? … . . (iii) 
 
?? ?? °
 for the following reaction ???????? + ?? ?? ?? ? ???????? + ?? ????
?? would be 
(a) +???????? ?? 
(b) -???????? ?? 
(c) +?????? ?? 
(d) -?????? ?? 
Ans: (d) 
?G
o
= 2? G
ZnO 
°
+ 2? G
SO
2
°
- 2? G
ZnS 
°
= [-616- 408] - [-293] = - 
731 J. 
Q5: The enthalpies of combustion of ?? (graphite) 
 and ?? (diamond) 
 are 393.5 and -?????? . ?? ???? /?????? 
respectively. The enthalpy of conversion of ?? (graphite) 
 to ?? (diamond) 
 in ???? /?????? is 
(a) -2.9 
(b) -888.9 
(c) 788.9 
(d) 1.9 
Ans: (d) 
C
graphite 
+ O
2
? CO
2
; ?H = -393.5
C
diamond 
+ O
2
? CO
2
; ?H = -395.4
 ? C
graphite 
C
diamond 
= -393.5 + 395.4 = ?? . ?? 
Q6: Which one of the following statement is false? 
(a) work is a state function. 
(b) temperature is a state function. 
(c) work appears at the boundary of the system. 
(d) change in the state is completely defined when the initial and final states are specified. 
Ans: (a) 
Q7: One mole of ice is converted into water at ?????? ?? . The  
?? ?? -?? respectively. The enthalpy 
change for the conversion is 
(a) ???? . ???? ?? ?????? -?? 
(b) ???????? ?? ???????? -?? 
(c) ?????? . ?? ?? ???????? -?? 
(d) ?????? . ?? ?? ???????? -?? 
Ans: (b) 
?G = ?H - T?S. At equilibrium ?G = 0, so ?H = T?S 
?H = 273 × (60.01 - 38.20) = 5954.13 J mole
-1
. 
Q8: The difference between heats of reaction at constant pressure and constant volume of the 
following reaction would be 
?? ?? ?? ?? ?? (?? ) + ???? ?? ?? ( ?? ) ? ???? ????
?? ( ?? ) + ?? ?? ?? ?? (?? )  at ????
°
?? 
in ???? ?????? -?? is 
(a) -7.43 
(b) +4.72 
(c) -5.72 
(d) +8.43 
Ans:  (a) 
?H = ?U + ?n
g
RT
 ? ?H - ?U = ?n
g
RT =
-3 × 8.314× 298
1000
= -?? . ???????? ???? ?????? -1
. 
 
Q9:  For which of the following change ?? ?? ? ?? ?? ? 
(A) ?? ?? ( ?? ) + ?? ?? ( ?? ) ? ?????? (?? ) 
(B) ?????? (???? ) + ???????? (???? ) ? ???????? (???? ) + ?? ?? ?? (?? ) 
(C) ?? (?? ) + ?? ?? ( ?? ) ? ????
?? ( ?? ) 
(D) ?? ?? ( ?? ) + ?? ?? ?? ( ?? ) ? ?? ????
?? ( ?? ) 
Ans: (D) ??? = ??? + ??? ?? ?
 
Page 4


JEE Solved Example on Thermodynamic 
JEE Mains 
Q1: Calculate the enthalpy of formation of ????
-
ions from the following thermochemical data: 
?? ?? ?? (?? )
? ?? (???? )
+
+ ????
-
(???? ) ; ?? ?? ?????? ?? °
= +???? . ???? ????
?? ?? ( ?? )
+
?? ?? ?? ?? (?? )
? ?? ?? ?? (?? )
; ?? ?? ?????? ?? °
= -?????? . ???? ????
 
(a) -?????? . ???? ???? 
(b) -?????? . ???? ???? 
(c) +?????? . ?? ???? 
(d) -?????? . ?? ???? 
Ans: (a) 
?H
°
= 57.32 = ? ?H
f
°
 (products ) - ? ?H
f
°
 (reactants )
57.32 = ?H
f
°
(OH
-
) + 285.83? H
f
°
(OH
-
) = -?????? . ???? ????
 
Q2: Using bond energy data, calculate heat of formation of isoprene  Given bond 
energy of C–H = 98.8 kcal, H–H = 104 kcal, C–C = 83 kcal, C=C = 147 kcal and ?H of C(s) ? C(g) = 171 
kcal 
(a) ???? . ?????????? ?????? -?? 
(b) ???? . ?????????? ?????? -?? 
(c) ?????????????? ?????? -?? 
(d) ?????????????? ?????? -?? 
Ans:  
?H = 5(171) + 4(104) - [(147 × 2) + (83 × 2) + (8 × 98.8)]
 = ???? . ?????????? 
 
 
 
 
 
 
 
Q3: One mole of magnesium in the vapour state absorbed 1300 ???? of energy. If the first and 
second ionization energies of ???? are 750 and ???????? ???? ?????? -?? respectively, the final composition 
of the mixture is 
(a) ???? %????
+
and ???? %????
+?? 
(b) ???? %????
+
and ???? %????
+?? 
(c) ???? %????
+
and ???? %????
+?? 
(d) ???? %????
+
and ???? %????
+?? 
Ans: (c) 
Mg ? Mg
+
+ e
-
 
To ionise one mole of Mg completely 750 kJ is spent and energy left = 550 kJ. 
1450 kJ ionises 1 mole of Mg
+1
 
550 kJ ionises 0.38 mole of Mg
+1
 
Mg
+
? Mg
+2
+ e
-
1
1 - 0.38 0.38
% of Mg
+
= ???? % and that of Mg
+2
= ???? %
 
Q4:  
 
?????? + ?? ?? ? ???????? ; ?? ?? ?? = -?????? ?? … . . . (i) 
?????? + ?? ?? ? ???????? ; ?? ?? ?? = -?????? ?? ?? ?? + ?? . . . (ii) 
?? ?? ?? ? ?? ????
?? ( ?? ); ?? ?? ?? = -?????? ?? … . . (iii) 
 
?? ?? °
 for the following reaction ???????? + ?? ?? ?? ? ???????? + ?? ????
?? would be 
(a) +???????? ?? 
(b) -???????? ?? 
(c) +?????? ?? 
(d) -?????? ?? 
Ans: (d) 
?G
o
= 2? G
ZnO 
°
+ 2? G
SO
2
°
- 2? G
ZnS 
°
= [-616- 408] - [-293] = - 
731 J. 
Q5: The enthalpies of combustion of ?? (graphite) 
 and ?? (diamond) 
 are 393.5 and -?????? . ?? ???? /?????? 
respectively. The enthalpy of conversion of ?? (graphite) 
 to ?? (diamond) 
 in ???? /?????? is 
(a) -2.9 
(b) -888.9 
(c) 788.9 
(d) 1.9 
Ans: (d) 
C
graphite 
+ O
2
? CO
2
; ?H = -393.5
C
diamond 
+ O
2
? CO
2
; ?H = -395.4
 ? C
graphite 
C
diamond 
= -393.5 + 395.4 = ?? . ?? 
Q6: Which one of the following statement is false? 
(a) work is a state function. 
(b) temperature is a state function. 
(c) work appears at the boundary of the system. 
(d) change in the state is completely defined when the initial and final states are specified. 
Ans: (a) 
Q7: One mole of ice is converted into water at ?????? ?? . The  
?? ?? -?? respectively. The enthalpy 
change for the conversion is 
(a) ???? . ???? ?? ?????? -?? 
(b) ???????? ?? ???????? -?? 
(c) ?????? . ?? ?? ???????? -?? 
(d) ?????? . ?? ?? ???????? -?? 
Ans: (b) 
?G = ?H - T?S. At equilibrium ?G = 0, so ?H = T?S 
?H = 273 × (60.01 - 38.20) = 5954.13 J mole
-1
. 
Q8: The difference between heats of reaction at constant pressure and constant volume of the 
following reaction would be 
?? ?? ?? ?? ?? (?? ) + ???? ?? ?? ( ?? ) ? ???? ????
?? ( ?? ) + ?? ?? ?? ?? (?? )  at ????
°
?? 
in ???? ?????? -?? is 
(a) -7.43 
(b) +4.72 
(c) -5.72 
(d) +8.43 
Ans:  (a) 
?H = ?U + ?n
g
RT
 ? ?H - ?U = ?n
g
RT =
-3 × 8.314× 298
1000
= -?? . ???????? ???? ?????? -1
. 
 
Q9:  For which of the following change ?? ?? ? ?? ?? ? 
(A) ?? ?? ( ?? ) + ?? ?? ( ?? ) ? ?????? (?? ) 
(B) ?????? (???? ) + ???????? (???? ) ? ???????? (???? ) + ?? ?? ?? (?? ) 
(C) ?? (?? ) + ?? ?? ( ?? ) ? ????
?? ( ?? ) 
(D) ?? ?? ( ?? ) + ?? ?? ?? ( ?? ) ? ?? ????
?? ( ?? ) 
Ans: (D) ??? = ??? + ??? ?? ?
 
 Case-I = ??? 9
= 2 - 1 - 1 = 0
 Case-II = ??? 9
= 0 - 0 = 0
 Case-III = ??? 9
= 1 - 1 = 0
 Case-IV = ??? 9
= 2 - 3 - 1 = -2 ? 0
 ? In option (?)??? = ??? 
 
 
 
 
Q10:  The reactions 
????
?? ( ?? ) + ????
?? ( ?? ) ? ????
?? ???? (?? ) + ?????? (?? ).
 has ???? = -???????????? Bond  Bond Energy ???????? ?? ?? -????
? ????
?? ?????????? ? ??????
?? ?????? ? ?? ?? ???? ?????
?? ?? : ?? = ?? : ?? 
From the given data, what is the bond enthalpy of ???? - ???? bond 
(A) ???????????? 
(B) ???????????? 
(C) ???? . ???????????? 
(D) ???? . ???????????? 
Ans:  (D) CH
4
+ Cl
2
 ? ? CH
3
Cl+ HCl 
?H = -25
 -25 = 4 × C - H + 4Cl
 -Cl- 3 × CH- 1C- Cl- 1H- Cl
 
 
Q11:  If ?? ?? , ?? ?? and ?? ?? are enthalpies of ?? - ?? , ?? = ?? and ?? - ?? bonds respectively, and ?? ?? is the 
enthalpy of vaporization of water, estimate the standard enthalpy of combustion of hydrogen 
(A) ?? ?? +
?? ?? ?? - ?? ?? ?? + ?? ?? 
(B) ?? ?? +
?? ?? ?? - ?? ?? ?? - ?? ?? 
(C) ?? ?? +
?? ?? ?? - ?? ?? + ?? ?? 
(D) ?? ?? ?? - ?? ?? -
?? ?? ?? - ?? ?? 
Ans: B 
Page 5


JEE Solved Example on Thermodynamic 
JEE Mains 
Q1: Calculate the enthalpy of formation of ????
-
ions from the following thermochemical data: 
?? ?? ?? (?? )
? ?? (???? )
+
+ ????
-
(???? ) ; ?? ?? ?????? ?? °
= +???? . ???? ????
?? ?? ( ?? )
+
?? ?? ?? ?? (?? )
? ?? ?? ?? (?? )
; ?? ?? ?????? ?? °
= -?????? . ???? ????
 
(a) -?????? . ???? ???? 
(b) -?????? . ???? ???? 
(c) +?????? . ?? ???? 
(d) -?????? . ?? ???? 
Ans: (a) 
?H
°
= 57.32 = ? ?H
f
°
 (products ) - ? ?H
f
°
 (reactants )
57.32 = ?H
f
°
(OH
-
) + 285.83? H
f
°
(OH
-
) = -?????? . ???? ????
 
Q2: Using bond energy data, calculate heat of formation of isoprene  Given bond 
energy of C–H = 98.8 kcal, H–H = 104 kcal, C–C = 83 kcal, C=C = 147 kcal and ?H of C(s) ? C(g) = 171 
kcal 
(a) ???? . ?????????? ?????? -?? 
(b) ???? . ?????????? ?????? -?? 
(c) ?????????????? ?????? -?? 
(d) ?????????????? ?????? -?? 
Ans:  
?H = 5(171) + 4(104) - [(147 × 2) + (83 × 2) + (8 × 98.8)]
 = ???? . ?????????? 
 
 
 
 
 
 
 
Q3: One mole of magnesium in the vapour state absorbed 1300 ???? of energy. If the first and 
second ionization energies of ???? are 750 and ???????? ???? ?????? -?? respectively, the final composition 
of the mixture is 
(a) ???? %????
+
and ???? %????
+?? 
(b) ???? %????
+
and ???? %????
+?? 
(c) ???? %????
+
and ???? %????
+?? 
(d) ???? %????
+
and ???? %????
+?? 
Ans: (c) 
Mg ? Mg
+
+ e
-
 
To ionise one mole of Mg completely 750 kJ is spent and energy left = 550 kJ. 
1450 kJ ionises 1 mole of Mg
+1
 
550 kJ ionises 0.38 mole of Mg
+1
 
Mg
+
? Mg
+2
+ e
-
1
1 - 0.38 0.38
% of Mg
+
= ???? % and that of Mg
+2
= ???? %
 
Q4:  
 
?????? + ?? ?? ? ???????? ; ?? ?? ?? = -?????? ?? … . . . (i) 
?????? + ?? ?? ? ???????? ; ?? ?? ?? = -?????? ?? ?? ?? + ?? . . . (ii) 
?? ?? ?? ? ?? ????
?? ( ?? ); ?? ?? ?? = -?????? ?? … . . (iii) 
 
?? ?? °
 for the following reaction ???????? + ?? ?? ?? ? ???????? + ?? ????
?? would be 
(a) +???????? ?? 
(b) -???????? ?? 
(c) +?????? ?? 
(d) -?????? ?? 
Ans: (d) 
?G
o
= 2? G
ZnO 
°
+ 2? G
SO
2
°
- 2? G
ZnS 
°
= [-616- 408] - [-293] = - 
731 J. 
Q5: The enthalpies of combustion of ?? (graphite) 
 and ?? (diamond) 
 are 393.5 and -?????? . ?? ???? /?????? 
respectively. The enthalpy of conversion of ?? (graphite) 
 to ?? (diamond) 
 in ???? /?????? is 
(a) -2.9 
(b) -888.9 
(c) 788.9 
(d) 1.9 
Ans: (d) 
C
graphite 
+ O
2
? CO
2
; ?H = -393.5
C
diamond 
+ O
2
? CO
2
; ?H = -395.4
 ? C
graphite 
C
diamond 
= -393.5 + 395.4 = ?? . ?? 
Q6: Which one of the following statement is false? 
(a) work is a state function. 
(b) temperature is a state function. 
(c) work appears at the boundary of the system. 
(d) change in the state is completely defined when the initial and final states are specified. 
Ans: (a) 
Q7: One mole of ice is converted into water at ?????? ?? . The  
?? ?? -?? respectively. The enthalpy 
change for the conversion is 
(a) ???? . ???? ?? ?????? -?? 
(b) ???????? ?? ???????? -?? 
(c) ?????? . ?? ?? ???????? -?? 
(d) ?????? . ?? ?? ???????? -?? 
Ans: (b) 
?G = ?H - T?S. At equilibrium ?G = 0, so ?H = T?S 
?H = 273 × (60.01 - 38.20) = 5954.13 J mole
-1
. 
Q8: The difference between heats of reaction at constant pressure and constant volume of the 
following reaction would be 
?? ?? ?? ?? ?? (?? ) + ???? ?? ?? ( ?? ) ? ???? ????
?? ( ?? ) + ?? ?? ?? ?? (?? )  at ????
°
?? 
in ???? ?????? -?? is 
(a) -7.43 
(b) +4.72 
(c) -5.72 
(d) +8.43 
Ans:  (a) 
?H = ?U + ?n
g
RT
 ? ?H - ?U = ?n
g
RT =
-3 × 8.314× 298
1000
= -?? . ???????? ???? ?????? -1
. 
 
Q9:  For which of the following change ?? ?? ? ?? ?? ? 
(A) ?? ?? ( ?? ) + ?? ?? ( ?? ) ? ?????? (?? ) 
(B) ?????? (???? ) + ???????? (???? ) ? ???????? (???? ) + ?? ?? ?? (?? ) 
(C) ?? (?? ) + ?? ?? ( ?? ) ? ????
?? ( ?? ) 
(D) ?? ?? ( ?? ) + ?? ?? ?? ( ?? ) ? ?? ????
?? ( ?? ) 
Ans: (D) ??? = ??? + ??? ?? ?
 
 Case-I = ??? 9
= 2 - 1 - 1 = 0
 Case-II = ??? 9
= 0 - 0 = 0
 Case-III = ??? 9
= 1 - 1 = 0
 Case-IV = ??? 9
= 2 - 3 - 1 = -2 ? 0
 ? In option (?)??? = ??? 
 
 
 
 
Q10:  The reactions 
????
?? ( ?? ) + ????
?? ( ?? ) ? ????
?? ???? (?? ) + ?????? (?? ).
 has ???? = -???????????? Bond  Bond Energy ???????? ?? ?? -????
? ????
?? ?????????? ? ??????
?? ?????? ? ?? ?? ???? ?????
?? ?? : ?? = ?? : ?? 
From the given data, what is the bond enthalpy of ???? - ???? bond 
(A) ???????????? 
(B) ???????????? 
(C) ???? . ???????????? 
(D) ???? . ???????????? 
Ans:  (D) CH
4
+ Cl
2
 ? ? CH
3
Cl+ HCl 
?H = -25
 -25 = 4 × C - H + 4Cl
 -Cl- 3 × CH- 1C- Cl- 1H- Cl
 
 
Q11:  If ?? ?? , ?? ?? and ?? ?? are enthalpies of ?? - ?? , ?? = ?? and ?? - ?? bonds respectively, and ?? ?? is the 
enthalpy of vaporization of water, estimate the standard enthalpy of combustion of hydrogen 
(A) ?? ?? +
?? ?? ?? - ?? ?? ?? + ?? ?? 
(B) ?? ?? +
?? ?? ?? - ?? ?? ?? - ?? ?? 
(C) ?? ?? +
?? ?? ?? - ?? ?? + ?? ?? 
(D) ?? ?? ?? - ?? ?? -
?? ?? ?? - ?? ?? 
Ans: B 
 
??? comb 
= ???? (?? - 11) + 1/2?? · ?? (?? = ?? - 2 × ?? · ?? (???? ) 
B.E. (vap) 
= ?? 1
+ ?? /2 - 2 × ?? 3
- ?? 4
 
 
 
Q12: For the allotropic change represented by the equation ?? (graphite) ? ?? (diamond), 
?? = ?? . ?? ???? . If ?? ?? of diamond and ?? ?? of graphite are separately burnt to yield ????
?? , the enthalpy 
liberated in first case is 
(A) Less than in the second case by ?? . ?? ???? 
(B) More than in the second case by ???? . ?? ???? 
(C) More than in the second case by ?? . ???? ???? 
(D) Less than in second case by ???? . ?? ???? 
Ans:  (C) 
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FAQs on Thermodynamics Solved Examples - Chemistry for JEE Main & Advanced

1. What is the first law of thermodynamics?
Ans. The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted from one form to another.
2. How is the second law of thermodynamics defined?
Ans. The second law of thermodynamics states that in any energy transfer or conversion, some energy is lost as heat. This law also defines the concept of entropy, which always increases in isolated systems.
3. What is the difference between an open and closed thermodynamic system?
Ans. In a closed system, energy can enter or leave the system, but not matter. In an open system, both energy and matter can be exchanged with the surroundings.
4. How is work defined in thermodynamics?
Ans. In thermodynamics, work is defined as the energy transferred by a force acting through a distance. It can be expressed as the product of force and distance.
5. Can you give an example of an application of thermodynamics in real life?
Ans. One common example of thermodynamics in real life is the operation of a refrigerator, which uses the principles of thermodynamics to transfer heat from inside the refrigerator to the outside, keeping the inside cool.
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