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# 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
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
?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
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
?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 )
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
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
?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
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
?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 )
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
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
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
(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
?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)
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
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
?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
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
?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 )
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
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
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
(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
?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)
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
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
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
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
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
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
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
?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
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
?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 )
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
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
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
(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
?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)
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
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
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
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
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
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
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
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
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
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
2
1
V
SnRln
V
??
Page 5

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
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
?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
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
?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 )
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
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
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
(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
?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)
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
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
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
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
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
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
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
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
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
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
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
?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
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)
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
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
?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
(1) +2900 kJ (2) –2900 kJ (3) –16.11 kJ (4) +16.11 kJ
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