Chemical Thermodynamics · JEE Main previous year questions

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2017 3 questions

Q682017 · 8 Apr 2017 · Shift 1
The enthalpy change on freezing of 1 mol of water at $5^{\circ} C$ to ice at $- 5^{\circ} C$ is : (Given $Δ_{fus} H = 6 kJ mo l^{- 1}$ at $0^{\circ} C$ , $C_{p} (H_{2} O, ℓ) = 75.3 J mo l^{- 1} K^{- 1}$ $C_{p} (H_{2} O, s) = 36.8 J mo l^{- 1} K^{- 1}$ )
1. A. $5.44 kJ mo l^{- 1}$
2. B. $5.81 kJ mo l^{- 1}$
3. C. $6.56 kJ mo l^{- 1}$
4. D. $6.00 kJ mo l^{- 1}$
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Answer: C
Q722017 · 8 Apr 2017 · Shift 1
Consider the following ionization enthalpies of two elements 'A' and 'B' . | Element | Ionization enthalpy (kJ/mol) | | | |---|---|---|---| | | $1^{st}$ | $2^{nd}$ | $3^{rd}$ | | A | 899 | 1757 | 14847 | | B | 737 | 1450 | 7731 | Which of the following statements is correct ?
1. A.Both ‘A’ and ‘B’ belong to group-1where ‘B’ comes below ‘A’.
2. B.Both ‘A’ and ‘B’ belong to group-1 where ‘A’ comes below ‘B’.
3. C.Both ‘A’ and ‘B’ belong to group-2 where ‘B’ comes below ‘A’.
4. D.Both ‘A’ and ‘B’ belong to group-2 where ‘A’ comes below ‘B’.
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Answer: C

2015 2 questions

Q642015 · 4 Apr 2015 · Shift 1
The standard Gibbs energy change at $300 K$ for the reaction $2 A ⇌ B + C$ is $2494.2 J$ . At a given time, the composition of the reaction mixture is $[A] = 1/2$ , $[B] = 2$ and $[C] = 1/2$ . The reaction proceeds in the: $[R = 8.314 J/K/mol, e = 2.718]$
1. A.reverse direction because $Q > K_{c}$
2. B.forward direction because $Q < K_{c}$
3. C.reverse direction because $Q < K_{c}$
4. D.forward direction because $Q > K_{c}$
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Answer: A
Q832015 · 4 Apr 2015 · Shift 1
Which one of the following alkaline earth metal sulphates has its hydration enthalpy greater than its lattice enthalpy?
1. A. $BeS O_{4}$
2. B. $BaS O_{4}$
3. C. $SrS O_{4}$
4. D. $CaS O_{4}$
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Answer: A

2014 1 question

Q632014 · 6 Apr 2014 · Shift 1
For complete combustion of ethanol, $C_{2} H_{5} OH (l) + 3 O_{2} (g) \to 2 C O_{2} (g) + 3 H_{2} O (l)$ the amount of heat produced as measured in bomb calorimeter, is $1364.47 kJ mo l^{- 1}$ at $2 5^{\circ} C$ . Assuming ideality the Enthalpy of combustion, $Δ_{C} H$ , for the reaction will be : ( $R = 8.314 J K^{- 1} mo l^{- 1}$ )
1. A. $- 1460.50 kJ mo l^{- 1}$
2. B. $- 1350.50 kJ mo l^{- 1}$
3. C. $- 1366.95 kJ mo l^{- 1}$
4. D. $- 1361.95 kJ mo l^{- 1}$
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Answer: C

2012 2 questions

Q642012 · 12 May 2012 · Shift 1
Which among the following elements has the highest first ionization enthalpy?
1. A.Nitrogen
2. B.Boron
3. C.Carbon
4. D.Oxygen
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Answer: A
Q652012 · 7 May 2012 · Shift 1
The entropy of a sample of a certain substance increases by $0.836 J K^{- 1}$ on adding reversibly 0.3344 J of heat at constant temperature. The temperature of the sample is:
1. A.2.5 K
2. B.0.3 K
3. C.0.016 K
4. D.0.4 K
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Answer: D

2010 2 questions

Q652010 · 25 Apr 2010 · Shift 1
For a particular reversible reaction at temperature T, $Δ H$ and $Δ S$ were found to be both +ve. If $T_{e}$ is the temperature at equilibrium, the reaction would be spontaneous when :
1. A. $T_{e} > T$
2. B. $T > T_{e}$
3. C. $T_{e}$ is 5 times $T$
4. D. $T = T_{e}$
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Answer: B
Q752010 · 25 Apr 2010 · Shift 1
The Gibbs energy for the decomposition of $A l_{2} O_{3}$ at $50 0^{\circ} C$ is as follows : $\frac{2}{3} A l_{2} O_{3} \to \frac{4}{3} Al + O_{2}, Δ_{r} G = + 966 kJ mo l^{- 1}$ The potential difference needed for electrolytic reduction of $A l_{2} O_{3}$ at $50 0^{\circ} C$ is at least :
1. A.4.5 V
2. B.3.0 V
3. C.2.5 V
4. D.5.0 V
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Answer: C

2009 3 questions

Q652009 · 27 Apr 2009 · Shift 1
On the basis of the following thermochemical data : $(Δ_{f} G^{o} H_{(a q)}^{+} = 0)$ $H_{2} O (l) \to H^{+} (aq) + O H^{-} (aq); ΔH = 57.32 kJ$ $H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l); ΔH = - 286.20 kJ$ The value of enthalpy of formation of $O H^{-}$ ion at $2 5^{\circ} C$ is :
1. A. $- 22.88 kJ$
2. B. $- 228.88 kJ$
3. C. $+ 228.88 kJ$
4. D. $- 343.52 kJ$
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Answer: B
Q732009 · 27 Apr 2009 · Shift 1
In a fuel cell methanol is used as fuel and oxygen gas is used as an oxidizer. The reaction is $C H_{3} OH (l) + 3/2 O_{2} \to C O_{2} (g) + 2 H_{2} O (l)$ At 298K standard Gibb's energies of formation for $C H_{3} OH (l)$ , $H_{2} O (l)$ and $C O_{2} (g)$ are -166.2, -237.2 and $- 394.4 kJ mo l^{- 1}$ respectively. If standard enthalpy of combustion of methanol is $- 726 kJ mo l^{- 1}$ , efficiency of the fuel cell will be
1. A. $87%$
2. B. $90%$
3. C. $97%$
4. D. $80%$
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Answer: C
Q862009 · 27 Apr 2009 · Shift 1
The bond dissociation energy of $B - F$ in $B F_{3}$ is $646 kJ mo l^{- 1}$ whereas that of $C - F$ in $C F_{4}$ is $515 kJ mo l^{- 1}$ . The correct reason for higher $B - F$ bond dissociation energy as compared to that of $C - F$ is :
1. A.smaller size of $B$ -atom as compared to that of $C$ -atom
2. B.stronger $σ$ bond between $B$ and $F$ in $B F_{3}$ as compared to that between $C$ and $F$ in $C F_{4}$
3. C.significant $p π - p π$ interaction between $B$ and $F$ in $B F_{3}$ whereas there is no possibility of such interaction between $C$ and $F$ in $C F_{4}$ .
4. D.lower degree of $p π - p π$ interaction between $B$ and $F$ in $B F_{3}$ than that between $C$ and $F$ in $C F_{4}$ .
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Answer: C

2006 1 question

Q1062006 · 29 Apr 2006 · Shift 1
The standard enthalpy of formation $Δ_{f} H^{o}$ at $298 K$ for methane, $C H_{4} (g)$ , is $- 74.8 kJ mo l^{- 1}$ . The additional information required to determine the average energy for $C - H$ bond formation would be :
1. A.the dissociation energy of $H_{2}$ and enthalpy of sublimation of carbon
2. B.latent heat of vapourization of methane
3. C.the first four ionization energies of carbon and electron gain enthalpy of hydrogen
4. D.the dissociation energy of hydrogen molecule, $H_{2}$
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Answer: A

2005 3 questions

Q1582005 · 28 Apr 2005 · Shift 1
Consider an endothermic reaction, $X \to Y$ with the activation energies $E_{b}$ and $E_{f}$ for the backward and forward reactions, respectively. In general :
1. A. $E_{b} < E_{f}$
2. B. $E_{b} > E_{f}$
3. C. $E_{b} = E_{f}$
4. D.There is no definite relation between $E_{b}$ and $E_{f}$
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Answer: A
Q1632005 · 28 Apr 2005 · Shift 1
The exothermic formation of $Cl F_{3}$ is represented by the equation: $C l_{2} (g) + 3 F_{2} (g) ⇌ 2Cl F_{3} (g); ΔH = - 329 kJ$ Which of the following will increase the quantity of $Cl F_{3}$ in an equilibrium mixture of $C l_{2}$ , $F_{2}$ and $Cl F_{3}$ ?
1. A.Increasing the temperature
2. B.Removing $C l_{2}$
3. C.Increasing the volume of the container
4. D.Adding $F_{2}$
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Answer: D
Q1772005 · 28 Apr 2005 · Shift 1
For a spontaneous reaction the $Δ G$ , equilibrium constant $(K)$ and $E_{ce l l}^{o}$ will be respectively
1. A.-ve, >1, +ve
2. B.+ve, >1, -ve
3. C.-ve, <1, -ve
4. D.-ve, >1, -ve
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Answer: A

2004 1 question

Q1562004 · 24 Apr 2004 · Shift 1
The formation of the oxide ion $O^{2 -} (g)$ requires first an exothermic and then an endothermic step as shown below $O_{(g)} + e^{-} = O_{(g)}^{-}$ $Δ H^{\circ} = - 142 kJmo l^{- 1}$ $O_{(g)}^{-} + e^{-} = O_{(g)}^{2 -}$ $Δ H^{\circ} = 844 kJmo l^{- 1}$ This is because
1. A. $O^{-}$ ion will tend to resist the addition of another electron
2. B.Oxygen has high electron affinity
3. C.Oxygen is more electronegative
4. D. $O^{-}$ ion has comparatively larger size than oxygen atom
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Answer: A

2002 1 question

Q1572002 · 27 Apr 2002 · Shift 1
A heat engine absorbs heat $Q_{1}$ at temperature $T_{1}$ and heat $Q_{2}$ at temperature $T_{2}$ . Work done by the engine is J $(Q_{1} + Q_{2})$ . This data :
1. A.violates 1 $^{s t}$ law of thermodynamics
2. B.violates 1 $^{s t}$ law of thermodynamics if $Q_{1}$ is +ve
3. C.violates 1 $^{s t}$ law of thermodynamics if $Q_{1}$ is -ve
4. D.does not violate 1 $^{s t}$ law of thermodynamics
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Answer: D