MCQ: Chapter 6 - Thermodynamics, Class 11, Chemistry JEE Notes | EduRev

JEE : MCQ: Chapter 6 - Thermodynamics, Class 11, Chemistry JEE Notes | EduRev

 Page 1


Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
Solutions
Chapter 6
Thermodynamics
SECTION - A
Objective Type Questions (One option is correct)
1. Bond energies of H – H bond is 80 kJ/mol, I – I bond is 100 kJ/mol and for H – I bond is
200 kJ/mol, the enthalpy of the reaction :
H
2
(g) + I
2
(g) ? 2HI(g) is
(1) –120 kJ (2) –220 kJ (3) +100 kJ (4) +120 kJ
Sol. Answer (2)
H
2 
(g) + I
2 
(g) ? 2HI (g)
?H = ?B.E
r
 – ?B.E
p
 = 80 + 100 – 2 × 200 = – 220 kJ
2. The enthalpy of formation of H
2
O(l) is –280.70 kJ/mol and enthalpy of neutralisation of a strong acid and strong
base is –56.70 kJ/mol. What is the enthalpy of formation of OH
–
 ions?
(1) –22.9 kJ/mol (2) –224 kJ/mol (3) –58.7 kJ/mol (4) –214 kJ/mol
Sol. Answer (2)
?H
f(OH¯)
 = – 280 – (56.70) = – 224 kJ/mole
3. The heat of neutralisation of a strong dibasic acid in dilute solution by NaOH is nearly
(1) –27.4 kcal/eq (2) 13.7 kcal/mol (3) –13.7 kcal/eq (4) –13.7 kcal/mol
Sol. Answer (3)
H
+
 + OH
–
 ? H
2
O ?H = – 13.7 kcal/eq
4. The heat released in neutralisation of HCl and NaOH is 13.7 kcal/mol, the heat released on neutralisation of NaOH
with CH
3
COOH is 3.7 kcal/mol. The ?H° of ionisation of CH
3
COOH is
(1) 10.2 kcal (2) 10 kcal (3) 3.7 kcal (4) 9.5 kcal
Sol. Answer (2)
?H = 13.7 – 3.7 = 10 kcal
5. Which of the following reactions represents the enthalpy of formation of water?
(1) H
+
(aq) + OH
–
(aq) ? H
2
O(l ) (2) H
2
(g) + ½O
2
(g) ? H
2
O(l )
(3) 2H
2
(g) + O
2
(g) ? 2H
2
O(l ) (4) 2H
+
(aq) + 2OH
–
(aq) ? 2H
2
O(l )
Sol. Answer (2)
Enthalpy associated with formation of one mole of water from its constituent elements in their natural states.
Page 2


Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
Solutions
Chapter 6
Thermodynamics
SECTION - A
Objective Type Questions (One option is correct)
1. Bond energies of H – H bond is 80 kJ/mol, I – I bond is 100 kJ/mol and for H – I bond is
200 kJ/mol, the enthalpy of the reaction :
H
2
(g) + I
2
(g) ? 2HI(g) is
(1) –120 kJ (2) –220 kJ (3) +100 kJ (4) +120 kJ
Sol. Answer (2)
H
2 
(g) + I
2 
(g) ? 2HI (g)
?H = ?B.E
r
 – ?B.E
p
 = 80 + 100 – 2 × 200 = – 220 kJ
2. The enthalpy of formation of H
2
O(l) is –280.70 kJ/mol and enthalpy of neutralisation of a strong acid and strong
base is –56.70 kJ/mol. What is the enthalpy of formation of OH
–
 ions?
(1) –22.9 kJ/mol (2) –224 kJ/mol (3) –58.7 kJ/mol (4) –214 kJ/mol
Sol. Answer (2)
?H
f(OH¯)
 = – 280 – (56.70) = – 224 kJ/mole
3. The heat of neutralisation of a strong dibasic acid in dilute solution by NaOH is nearly
(1) –27.4 kcal/eq (2) 13.7 kcal/mol (3) –13.7 kcal/eq (4) –13.7 kcal/mol
Sol. Answer (3)
H
+
 + OH
–
 ? H
2
O ?H = – 13.7 kcal/eq
4. The heat released in neutralisation of HCl and NaOH is 13.7 kcal/mol, the heat released on neutralisation of NaOH
with CH
3
COOH is 3.7 kcal/mol. The ?H° of ionisation of CH
3
COOH is
(1) 10.2 kcal (2) 10 kcal (3) 3.7 kcal (4) 9.5 kcal
Sol. Answer (2)
?H = 13.7 – 3.7 = 10 kcal
5. Which of the following reactions represents the enthalpy of formation of water?
(1) H
+
(aq) + OH
–
(aq) ? H
2
O(l ) (2) H
2
(g) + ½O
2
(g) ? H
2
O(l )
(3) 2H
2
(g) + O
2
(g) ? 2H
2
O(l ) (4) 2H
+
(aq) + 2OH
–
(aq) ? 2H
2
O(l )
Sol. Answer (2)
Enthalpy associated with formation of one mole of water from its constituent elements in their natural states.
40 Thermodynamics Solution of Assignment (Set-2)
Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
6. The energy required to break 76 gm gaseous fluorine into free gaseous atom is 180 kcal at 25°C. The bond
energy of F – F bond will be
(1) 180 kcal (2) 90 kcal (3) 45 kcal (4) 104 kcal
Sol. Answer (2)
2
38g
F2F ?
? 76 g F
2
 needs 180 kcal energy
? 38 g F
2
 needs energy = 
180
38
76
?
 = 90 kcal
7. For the reaction 2HgO(s) ? 2Hg(l ) + O
2
(g)
(1) ?H > 0 and ?S < 0 (2) ?H > 0 and ?S > 0
(3) ?H < 0 and ?S < 0 (4) ?H < 0 and ?S > 0
Sol. Answer (2)
2HgO(s) ? 2Hg(l) + O
2
(g)
It is endothermic and spontaneous process [? ? n
g
 > 0]
??H > 0 and ?S > 0
8. The heat of combustion of yellow phosphorus and red phosphorus are –9.91 kJ/mol and – 8.78 kJ/mol
respectively. Then the heat of transition of yellow phosphorus to red phosphorus is
(1) –18.69 kJ (2) +1.13 kJ (3) +18.69 kJ (4) –1.13 kJ
Sol. Answer (4)
(yellow) (red)
PP ?
?H
Transition 
= – 9.91 – (–8.78) = – 1.13 kJ
9. If the entropy of vaporisation of a liquid is 110 JK
–1
 mol
–1
 and its enthalpy of vaporisation is 50 kJmol
–1
. The
boiling point of the liquid is
(1) 354.5 K (2) 454.5 K (3) 554.5 K (4) 445.5 K
Sol. Answer (2)
?S
vap
 = 110 J/K/mol
?H
vap 
= 50 × 10
3
 J/mol
?S = 
B.P.
H
T
?
3
B.P.
50 10
T
110
?
? = 454.54 K
10. Which of the following represents heat of formation ( ?H
f
)?
(1) C(diamond) + O
2
(g) ? CO
2
(g) (2) 2CO(g) + O
2
(g) ? 2CO
2
(g)
(3) ½H
2
(g) + ½F
2
(g) ? HF(g) (4) N
2
(g) + 3H
2
(g) ? 2NH
3
(g)
Sol. Answer (3)
There is formation of one mole of gas from its constituent elements in their standard states.
22
11
H(g) F(g) HF(g)
22
??
Page 3


Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
Solutions
Chapter 6
Thermodynamics
SECTION - A
Objective Type Questions (One option is correct)
1. Bond energies of H – H bond is 80 kJ/mol, I – I bond is 100 kJ/mol and for H – I bond is
200 kJ/mol, the enthalpy of the reaction :
H
2
(g) + I
2
(g) ? 2HI(g) is
(1) –120 kJ (2) –220 kJ (3) +100 kJ (4) +120 kJ
Sol. Answer (2)
H
2 
(g) + I
2 
(g) ? 2HI (g)
?H = ?B.E
r
 – ?B.E
p
 = 80 + 100 – 2 × 200 = – 220 kJ
2. The enthalpy of formation of H
2
O(l) is –280.70 kJ/mol and enthalpy of neutralisation of a strong acid and strong
base is –56.70 kJ/mol. What is the enthalpy of formation of OH
–
 ions?
(1) –22.9 kJ/mol (2) –224 kJ/mol (3) –58.7 kJ/mol (4) –214 kJ/mol
Sol. Answer (2)
?H
f(OH¯)
 = – 280 – (56.70) = – 224 kJ/mole
3. The heat of neutralisation of a strong dibasic acid in dilute solution by NaOH is nearly
(1) –27.4 kcal/eq (2) 13.7 kcal/mol (3) –13.7 kcal/eq (4) –13.7 kcal/mol
Sol. Answer (3)
H
+
 + OH
–
 ? H
2
O ?H = – 13.7 kcal/eq
4. The heat released in neutralisation of HCl and NaOH is 13.7 kcal/mol, the heat released on neutralisation of NaOH
with CH
3
COOH is 3.7 kcal/mol. The ?H° of ionisation of CH
3
COOH is
(1) 10.2 kcal (2) 10 kcal (3) 3.7 kcal (4) 9.5 kcal
Sol. Answer (2)
?H = 13.7 – 3.7 = 10 kcal
5. Which of the following reactions represents the enthalpy of formation of water?
(1) H
+
(aq) + OH
–
(aq) ? H
2
O(l ) (2) H
2
(g) + ½O
2
(g) ? H
2
O(l )
(3) 2H
2
(g) + O
2
(g) ? 2H
2
O(l ) (4) 2H
+
(aq) + 2OH
–
(aq) ? 2H
2
O(l )
Sol. Answer (2)
Enthalpy associated with formation of one mole of water from its constituent elements in their natural states.
40 Thermodynamics Solution of Assignment (Set-2)
Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
6. The energy required to break 76 gm gaseous fluorine into free gaseous atom is 180 kcal at 25°C. The bond
energy of F – F bond will be
(1) 180 kcal (2) 90 kcal (3) 45 kcal (4) 104 kcal
Sol. Answer (2)
2
38g
F2F ?
? 76 g F
2
 needs 180 kcal energy
? 38 g F
2
 needs energy = 
180
38
76
?
 = 90 kcal
7. For the reaction 2HgO(s) ? 2Hg(l ) + O
2
(g)
(1) ?H > 0 and ?S < 0 (2) ?H > 0 and ?S > 0
(3) ?H < 0 and ?S < 0 (4) ?H < 0 and ?S > 0
Sol. Answer (2)
2HgO(s) ? 2Hg(l) + O
2
(g)
It is endothermic and spontaneous process [? ? n
g
 > 0]
??H > 0 and ?S > 0
8. The heat of combustion of yellow phosphorus and red phosphorus are –9.91 kJ/mol and – 8.78 kJ/mol
respectively. Then the heat of transition of yellow phosphorus to red phosphorus is
(1) –18.69 kJ (2) +1.13 kJ (3) +18.69 kJ (4) –1.13 kJ
Sol. Answer (4)
(yellow) (red)
PP ?
?H
Transition 
= – 9.91 – (–8.78) = – 1.13 kJ
9. If the entropy of vaporisation of a liquid is 110 JK
–1
 mol
–1
 and its enthalpy of vaporisation is 50 kJmol
–1
. The
boiling point of the liquid is
(1) 354.5 K (2) 454.5 K (3) 554.5 K (4) 445.5 K
Sol. Answer (2)
?S
vap
 = 110 J/K/mol
?H
vap 
= 50 × 10
3
 J/mol
?S = 
B.P.
H
T
?
3
B.P.
50 10
T
110
?
? = 454.54 K
10. Which of the following represents heat of formation ( ?H
f
)?
(1) C(diamond) + O
2
(g) ? CO
2
(g) (2) 2CO(g) + O
2
(g) ? 2CO
2
(g)
(3) ½H
2
(g) + ½F
2
(g) ? HF(g) (4) N
2
(g) + 3H
2
(g) ? 2NH
3
(g)
Sol. Answer (3)
There is formation of one mole of gas from its constituent elements in their standard states.
22
11
H(g) F(g) HF(g)
22
??
41 Solution of Assignment (Set-2) Thermodynamics
Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
11. 1 mole of an ideal gas is expanded from an initial pressure of 1 bar to final pressure of 0.1 bar at constant
temperature of 273 K. Predict which of the following is not true?
(1) ?E = 0 (2) ?H = 0 (3) PV is constant (4) ?S < 0
Sol. Answer (4)
For an isothermal process, ?E = 0, PV = constant, ?H = 0 and ?S > 0.
12. Which of the following conditions should be satisfied for the given reaction to be spontaneous at 0°C and 1 atm?
H
2
O(s)  H
2
O(l )
(1) ?H = ?G (2) ?H < T ?S (3) ?H > T ?S (4) ?H = T ?S
Sol. Answer (2)
If ?H < T ?S
The ?G < 0 (–ve) and reaction will be spontaneous
13. The heat of formation of CO
2
 is –407 kJ/mol. The energy required for the process
3CO
2
(g) ? 3C(g) + 2O
3
(g) is
(1) Less than 1221 kJ (2) More than 1221 kJ
(3) Is equal to 1221 kJ (4) Cannot be predicted
Sol. Answer (2)
2
f(CO )
H ?
 for 3 moles will be 
 
= 3 × 407 = 1221 kJ
? With O
3
 it should be greater than 1221 kJ
14. The free energy change due to a reaction is zero when
(1) The reactants are initially mixed (2) A catalyst is added
(3) The system is at equilibrium (4) The reactants are completely consumed
Sol. Answer (3)
At equilibrium ?G = 0
15. From the given graph
Free energy
Reactant Product
C
B
A
Which of the following statement is correct?
(1) The point B represents the state of equilibrium
(2) The equilibrium composition strongly favours the reactant
(3) From the point B formation of product is equally spontaneous as of reactant
(4) From the point B formation of reactant is more spontaneous than that of product
Sol. Answer (1)
At equilibrium ?G = 0
Page 4


Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
Solutions
Chapter 6
Thermodynamics
SECTION - A
Objective Type Questions (One option is correct)
1. Bond energies of H – H bond is 80 kJ/mol, I – I bond is 100 kJ/mol and for H – I bond is
200 kJ/mol, the enthalpy of the reaction :
H
2
(g) + I
2
(g) ? 2HI(g) is
(1) –120 kJ (2) –220 kJ (3) +100 kJ (4) +120 kJ
Sol. Answer (2)
H
2 
(g) + I
2 
(g) ? 2HI (g)
?H = ?B.E
r
 – ?B.E
p
 = 80 + 100 – 2 × 200 = – 220 kJ
2. The enthalpy of formation of H
2
O(l) is –280.70 kJ/mol and enthalpy of neutralisation of a strong acid and strong
base is –56.70 kJ/mol. What is the enthalpy of formation of OH
–
 ions?
(1) –22.9 kJ/mol (2) –224 kJ/mol (3) –58.7 kJ/mol (4) –214 kJ/mol
Sol. Answer (2)
?H
f(OH¯)
 = – 280 – (56.70) = – 224 kJ/mole
3. The heat of neutralisation of a strong dibasic acid in dilute solution by NaOH is nearly
(1) –27.4 kcal/eq (2) 13.7 kcal/mol (3) –13.7 kcal/eq (4) –13.7 kcal/mol
Sol. Answer (3)
H
+
 + OH
–
 ? H
2
O ?H = – 13.7 kcal/eq
4. The heat released in neutralisation of HCl and NaOH is 13.7 kcal/mol, the heat released on neutralisation of NaOH
with CH
3
COOH is 3.7 kcal/mol. The ?H° of ionisation of CH
3
COOH is
(1) 10.2 kcal (2) 10 kcal (3) 3.7 kcal (4) 9.5 kcal
Sol. Answer (2)
?H = 13.7 – 3.7 = 10 kcal
5. Which of the following reactions represents the enthalpy of formation of water?
(1) H
+
(aq) + OH
–
(aq) ? H
2
O(l ) (2) H
2
(g) + ½O
2
(g) ? H
2
O(l )
(3) 2H
2
(g) + O
2
(g) ? 2H
2
O(l ) (4) 2H
+
(aq) + 2OH
–
(aq) ? 2H
2
O(l )
Sol. Answer (2)
Enthalpy associated with formation of one mole of water from its constituent elements in their natural states.
40 Thermodynamics Solution of Assignment (Set-2)
Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
6. The energy required to break 76 gm gaseous fluorine into free gaseous atom is 180 kcal at 25°C. The bond
energy of F – F bond will be
(1) 180 kcal (2) 90 kcal (3) 45 kcal (4) 104 kcal
Sol. Answer (2)
2
38g
F2F ?
? 76 g F
2
 needs 180 kcal energy
? 38 g F
2
 needs energy = 
180
38
76
?
 = 90 kcal
7. For the reaction 2HgO(s) ? 2Hg(l ) + O
2
(g)
(1) ?H > 0 and ?S < 0 (2) ?H > 0 and ?S > 0
(3) ?H < 0 and ?S < 0 (4) ?H < 0 and ?S > 0
Sol. Answer (2)
2HgO(s) ? 2Hg(l) + O
2
(g)
It is endothermic and spontaneous process [? ? n
g
 > 0]
??H > 0 and ?S > 0
8. The heat of combustion of yellow phosphorus and red phosphorus are –9.91 kJ/mol and – 8.78 kJ/mol
respectively. Then the heat of transition of yellow phosphorus to red phosphorus is
(1) –18.69 kJ (2) +1.13 kJ (3) +18.69 kJ (4) –1.13 kJ
Sol. Answer (4)
(yellow) (red)
PP ?
?H
Transition 
= – 9.91 – (–8.78) = – 1.13 kJ
9. If the entropy of vaporisation of a liquid is 110 JK
–1
 mol
–1
 and its enthalpy of vaporisation is 50 kJmol
–1
. The
boiling point of the liquid is
(1) 354.5 K (2) 454.5 K (3) 554.5 K (4) 445.5 K
Sol. Answer (2)
?S
vap
 = 110 J/K/mol
?H
vap 
= 50 × 10
3
 J/mol
?S = 
B.P.
H
T
?
3
B.P.
50 10
T
110
?
? = 454.54 K
10. Which of the following represents heat of formation ( ?H
f
)?
(1) C(diamond) + O
2
(g) ? CO
2
(g) (2) 2CO(g) + O
2
(g) ? 2CO
2
(g)
(3) ½H
2
(g) + ½F
2
(g) ? HF(g) (4) N
2
(g) + 3H
2
(g) ? 2NH
3
(g)
Sol. Answer (3)
There is formation of one mole of gas from its constituent elements in their standard states.
22
11
H(g) F(g) HF(g)
22
??
41 Solution of Assignment (Set-2) Thermodynamics
Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
11. 1 mole of an ideal gas is expanded from an initial pressure of 1 bar to final pressure of 0.1 bar at constant
temperature of 273 K. Predict which of the following is not true?
(1) ?E = 0 (2) ?H = 0 (3) PV is constant (4) ?S < 0
Sol. Answer (4)
For an isothermal process, ?E = 0, PV = constant, ?H = 0 and ?S > 0.
12. Which of the following conditions should be satisfied for the given reaction to be spontaneous at 0°C and 1 atm?
H
2
O(s)  H
2
O(l )
(1) ?H = ?G (2) ?H < T ?S (3) ?H > T ?S (4) ?H = T ?S
Sol. Answer (2)
If ?H < T ?S
The ?G < 0 (–ve) and reaction will be spontaneous
13. The heat of formation of CO
2
 is –407 kJ/mol. The energy required for the process
3CO
2
(g) ? 3C(g) + 2O
3
(g) is
(1) Less than 1221 kJ (2) More than 1221 kJ
(3) Is equal to 1221 kJ (4) Cannot be predicted
Sol. Answer (2)
2
f(CO )
H ?
 for 3 moles will be 
 
= 3 × 407 = 1221 kJ
? With O
3
 it should be greater than 1221 kJ
14. The free energy change due to a reaction is zero when
(1) The reactants are initially mixed (2) A catalyst is added
(3) The system is at equilibrium (4) The reactants are completely consumed
Sol. Answer (3)
At equilibrium ?G = 0
15. From the given graph
Free energy
Reactant Product
C
B
A
Which of the following statement is correct?
(1) The point B represents the state of equilibrium
(2) The equilibrium composition strongly favours the reactant
(3) From the point B formation of product is equally spontaneous as of reactant
(4) From the point B formation of reactant is more spontaneous than that of product
Sol. Answer (1)
At equilibrium ?G = 0
42 Thermodynamics Solution of Assignment (Set-2)
Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
16. The heat of combustion of sucrose C
12
H
22
O
11
 (s) at constant volume is –1348.9 kcal mol
–1
 at 25°C, then the heat
of reaction at constant pressure, is
(1) – 1348.9 kcal (2) – 1342.344 kcal (3) 1250 kcal (4) – 1250 kcal
Sol. Answer (1)
12 22 11 2 2 2
(s) (g) (g) (l)
C H O  12O  12CO  11 H O ?????
17. For the reaction,
78 2 2 2
C H (l) 9O (g) 7CO (g) 4H O(l), ?????
the calculated heat of reaction is 232 kJ mol
–1
 and observed heat of reaction is 50.4 kJ mol
–1
, then the resonance
energy is
(1) – 181.6 kJ mol
–1
(2) + 181.6 kJ mol
–1
(3) 172 kJ mol
–1
(4) – 172 kJ mol
–1
Sol. Answer (1)
Resonance Energy = –232 – (–50.4)
= –182.2 kJ mol
–1
18. Given that
A(s) A(l) ?? ?
?H = x
A(l) A(g) ?? ?
?H = y
The heat of sublimation of A will be
(1) x – y (2) x + y (3) x or y (4) – x + y
Sol. Answer (2)
According to Hess’s law 
sub
Hxy ???
19. AB, A
2
 and B
2
 are diatomic molecules. If the bond enthalpies of A
2
, AB and B
2
 are in the ratio 1 : 1 : 0.5 and
enthalpy of formation of AB from A
2
 and B
2
 is –100  kJ mol
–1
. What is the bond enthalpy of A
2
?
(1) 400 kJ mol
–1
(2) 200 kJ mol
–1
(3) 300 kJ mol
–1
(4) 100 kJ mol
–1
Sol. Answer (1)
22
11 1
AB AB
22 2
??? ?
22
11
H B.E. of H B.E. of B B.E. of A–B
22
?? ? ?
20. One mole of a perfect gas expands isothermally to ten times of its original volume. The change in entropy is
(1) 0.1 R (2) 10 R (3) 2 R (4) 2.303 R
Sol. Answer (4)
2
1
V
SnRln
V
??
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Solutions
Chapter 6
Thermodynamics
SECTION - A
Objective Type Questions (One option is correct)
1. Bond energies of H – H bond is 80 kJ/mol, I – I bond is 100 kJ/mol and for H – I bond is
200 kJ/mol, the enthalpy of the reaction :
H
2
(g) + I
2
(g) ? 2HI(g) is
(1) –120 kJ (2) –220 kJ (3) +100 kJ (4) +120 kJ
Sol. Answer (2)
H
2 
(g) + I
2 
(g) ? 2HI (g)
?H = ?B.E
r
 – ?B.E
p
 = 80 + 100 – 2 × 200 = – 220 kJ
2. The enthalpy of formation of H
2
O(l) is –280.70 kJ/mol and enthalpy of neutralisation of a strong acid and strong
base is –56.70 kJ/mol. What is the enthalpy of formation of OH
–
 ions?
(1) –22.9 kJ/mol (2) –224 kJ/mol (3) –58.7 kJ/mol (4) –214 kJ/mol
Sol. Answer (2)
?H
f(OH¯)
 = – 280 – (56.70) = – 224 kJ/mole
3. The heat of neutralisation of a strong dibasic acid in dilute solution by NaOH is nearly
(1) –27.4 kcal/eq (2) 13.7 kcal/mol (3) –13.7 kcal/eq (4) –13.7 kcal/mol
Sol. Answer (3)
H
+
 + OH
–
 ? H
2
O ?H = – 13.7 kcal/eq
4. The heat released in neutralisation of HCl and NaOH is 13.7 kcal/mol, the heat released on neutralisation of NaOH
with CH
3
COOH is 3.7 kcal/mol. The ?H° of ionisation of CH
3
COOH is
(1) 10.2 kcal (2) 10 kcal (3) 3.7 kcal (4) 9.5 kcal
Sol. Answer (2)
?H = 13.7 – 3.7 = 10 kcal
5. Which of the following reactions represents the enthalpy of formation of water?
(1) H
+
(aq) + OH
–
(aq) ? H
2
O(l ) (2) H
2
(g) + ½O
2
(g) ? H
2
O(l )
(3) 2H
2
(g) + O
2
(g) ? 2H
2
O(l ) (4) 2H
+
(aq) + 2OH
–
(aq) ? 2H
2
O(l )
Sol. Answer (2)
Enthalpy associated with formation of one mole of water from its constituent elements in their natural states.
40 Thermodynamics Solution of Assignment (Set-2)
Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
6. The energy required to break 76 gm gaseous fluorine into free gaseous atom is 180 kcal at 25°C. The bond
energy of F – F bond will be
(1) 180 kcal (2) 90 kcal (3) 45 kcal (4) 104 kcal
Sol. Answer (2)
2
38g
F2F ?
? 76 g F
2
 needs 180 kcal energy
? 38 g F
2
 needs energy = 
180
38
76
?
 = 90 kcal
7. For the reaction 2HgO(s) ? 2Hg(l ) + O
2
(g)
(1) ?H > 0 and ?S < 0 (2) ?H > 0 and ?S > 0
(3) ?H < 0 and ?S < 0 (4) ?H < 0 and ?S > 0
Sol. Answer (2)
2HgO(s) ? 2Hg(l) + O
2
(g)
It is endothermic and spontaneous process [? ? n
g
 > 0]
??H > 0 and ?S > 0
8. The heat of combustion of yellow phosphorus and red phosphorus are –9.91 kJ/mol and – 8.78 kJ/mol
respectively. Then the heat of transition of yellow phosphorus to red phosphorus is
(1) –18.69 kJ (2) +1.13 kJ (3) +18.69 kJ (4) –1.13 kJ
Sol. Answer (4)
(yellow) (red)
PP ?
?H
Transition 
= – 9.91 – (–8.78) = – 1.13 kJ
9. If the entropy of vaporisation of a liquid is 110 JK
–1
 mol
–1
 and its enthalpy of vaporisation is 50 kJmol
–1
. The
boiling point of the liquid is
(1) 354.5 K (2) 454.5 K (3) 554.5 K (4) 445.5 K
Sol. Answer (2)
?S
vap
 = 110 J/K/mol
?H
vap 
= 50 × 10
3
 J/mol
?S = 
B.P.
H
T
?
3
B.P.
50 10
T
110
?
? = 454.54 K
10. Which of the following represents heat of formation ( ?H
f
)?
(1) C(diamond) + O
2
(g) ? CO
2
(g) (2) 2CO(g) + O
2
(g) ? 2CO
2
(g)
(3) ½H
2
(g) + ½F
2
(g) ? HF(g) (4) N
2
(g) + 3H
2
(g) ? 2NH
3
(g)
Sol. Answer (3)
There is formation of one mole of gas from its constituent elements in their standard states.
22
11
H(g) F(g) HF(g)
22
??
41 Solution of Assignment (Set-2) Thermodynamics
Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
11. 1 mole of an ideal gas is expanded from an initial pressure of 1 bar to final pressure of 0.1 bar at constant
temperature of 273 K. Predict which of the following is not true?
(1) ?E = 0 (2) ?H = 0 (3) PV is constant (4) ?S < 0
Sol. Answer (4)
For an isothermal process, ?E = 0, PV = constant, ?H = 0 and ?S > 0.
12. Which of the following conditions should be satisfied for the given reaction to be spontaneous at 0°C and 1 atm?
H
2
O(s)  H
2
O(l )
(1) ?H = ?G (2) ?H < T ?S (3) ?H > T ?S (4) ?H = T ?S
Sol. Answer (2)
If ?H < T ?S
The ?G < 0 (–ve) and reaction will be spontaneous
13. The heat of formation of CO
2
 is –407 kJ/mol. The energy required for the process
3CO
2
(g) ? 3C(g) + 2O
3
(g) is
(1) Less than 1221 kJ (2) More than 1221 kJ
(3) Is equal to 1221 kJ (4) Cannot be predicted
Sol. Answer (2)
2
f(CO )
H ?
 for 3 moles will be 
 
= 3 × 407 = 1221 kJ
? With O
3
 it should be greater than 1221 kJ
14. The free energy change due to a reaction is zero when
(1) The reactants are initially mixed (2) A catalyst is added
(3) The system is at equilibrium (4) The reactants are completely consumed
Sol. Answer (3)
At equilibrium ?G = 0
15. From the given graph
Free energy
Reactant Product
C
B
A
Which of the following statement is correct?
(1) The point B represents the state of equilibrium
(2) The equilibrium composition strongly favours the reactant
(3) From the point B formation of product is equally spontaneous as of reactant
(4) From the point B formation of reactant is more spontaneous than that of product
Sol. Answer (1)
At equilibrium ?G = 0
42 Thermodynamics Solution of Assignment (Set-2)
Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
16. The heat of combustion of sucrose C
12
H
22
O
11
 (s) at constant volume is –1348.9 kcal mol
–1
 at 25°C, then the heat
of reaction at constant pressure, is
(1) – 1348.9 kcal (2) – 1342.344 kcal (3) 1250 kcal (4) – 1250 kcal
Sol. Answer (1)
12 22 11 2 2 2
(s) (g) (g) (l)
C H O  12O  12CO  11 H O ?????
17. For the reaction,
78 2 2 2
C H (l) 9O (g) 7CO (g) 4H O(l), ?????
the calculated heat of reaction is 232 kJ mol
–1
 and observed heat of reaction is 50.4 kJ mol
–1
, then the resonance
energy is
(1) – 181.6 kJ mol
–1
(2) + 181.6 kJ mol
–1
(3) 172 kJ mol
–1
(4) – 172 kJ mol
–1
Sol. Answer (1)
Resonance Energy = –232 – (–50.4)
= –182.2 kJ mol
–1
18. Given that
A(s) A(l) ?? ?
?H = x
A(l) A(g) ?? ?
?H = y
The heat of sublimation of A will be
(1) x – y (2) x + y (3) x or y (4) – x + y
Sol. Answer (2)
According to Hess’s law 
sub
Hxy ???
19. AB, A
2
 and B
2
 are diatomic molecules. If the bond enthalpies of A
2
, AB and B
2
 are in the ratio 1 : 1 : 0.5 and
enthalpy of formation of AB from A
2
 and B
2
 is –100  kJ mol
–1
. What is the bond enthalpy of A
2
?
(1) 400 kJ mol
–1
(2) 200 kJ mol
–1
(3) 300 kJ mol
–1
(4) 100 kJ mol
–1
Sol. Answer (1)
22
11 1
AB AB
22 2
??? ?
22
11
H B.E. of H B.E. of B B.E. of A–B
22
?? ? ?
20. One mole of a perfect gas expands isothermally to ten times of its original volume. The change in entropy is
(1) 0.1 R (2) 10 R (3) 2 R (4) 2.303 R
Sol. Answer (4)
2
1
V
SnRln
V
??
43 Solution of Assignment (Set-2) Thermodynamics
Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash T ower, Plot No.-4, Sector-1 1, Dwarka, New Delhi-75 Ph.01 1-47623456
21. The value of log
10
 K for a reaction A  B is
(Given : ?
r
H°
298K
 = –54.07 kJ mol
–1
, ?
r
S°
298K 
= 10 JK 
–1 
mol
–1 
and R = 8.314 JK
–1
mol
–1
; 2.303 × 8.314 × 298 = 5705)
[IIT-JEE 2007]
(1) 5 (2) 10 (3) 95 (4) 100
Sol. Answer (2)
?G° = ?H° – T ?S° = –2.303 RT log
10
K
= – 54.07 × 10
3
 – 298 × 10 = – 57050 JK
–1
mol
–1
?G° = – 2.303 RT log
10
K
– 57050 = –2.303 × 8.314 × 298 log
10
K
? 10 = log
10
K
22. For the process H
2
O(l) (1 bar, 373 K) ? H
2
O(g) (1 bar, 373 K), the correct set of thermodynamics parameters
is [IIT-JEE 2007]
(1) ?G = 0, ?S = +ve (2) ?G = 0, ?S = –ve
(3) ?G = +ve, ?S = 0 (4) ?G = –ve, ?S = +ve
Sol. Answer (1)
At 373 K H
2
O(l) is in equilibrium with H
2
O(g).
23. The species which by definition has ZERO standard molar enthalpy of formation at 298 K is
[IIT-JEE 2010]
(1) Br
2
(g) (2) Cl
2
(g) (3) H
2
O(g) (4) CH
4
(g)
Sol. Answer (2)
Cl
2
 is considered as standard state of chlorine and enthalpy of formation in standard state is zero (assumed).
24. The bond energy (in kcal mol
–1
) of a C—C single bond is approximately [IIT-JEE 2010]
(1) 1 (2) 10 (3) 100 (4) 1000
Sol. Answer (3)
Bond energy of C—C is considered to be 100 kcal mol
–1
 approximately.
25. Using the data provided, calculate the multiple bond energy (kJ mol
–1
) of a C ? C bond in C
2
H
2
. That energy is
(take the bond energy of a C – H bond as 350 kJ mol
–1
) [IIT-JEE 2012]
222
2C(s) H (g) C H (g) ??? ? ?H = 225 kJ mol
–1
2C(s) 2C(g) ? ? ? ?H = 1410 kJ mol
–1
2
H(g) 2H(g) ? ? ? ?H = 330 kJ mol
–1
(1) 1 165 (2) 837 (3) 865 (4) 815
Sol. Answer (4)
?H = Bond energy in reactant – Bond energy in product
? 225 = (1410 + 330) – (700 + ?H
C ? C
)
??H
C ?C
 = 1740 – 925 = 815 kJ/mol
26. The standard enthalpies of formation of CO
2
(g), H
2
O(l) and glucose(s) at 25°C are –400 kJ/mol,
–300 kJ/mol and –1300 kJ/mol, respectively. The standard enthalpy of combustion per gram of glucose at 25°C
is [JEE(Advanced)-2013]
(1) +2900 kJ (2) –2900 kJ (3) –16.11 kJ (4) +16.11 kJ
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