Q. No.Which of the following is true for an endothermic reaction that is non-spontaneous at the freezing point of water and spontaneous at the boiling point of water?
| 1. | Both \(\Delta H\) and \(\Delta S\) are positive |
| 2. | \(\Delta H\) is negative but \(\Delta S\) is positive |
| 3. | \(\Delta H\) is positive but \(\Delta S\) is negative |
| 4. | Both \(\Delta H\) and \(\Delta S\) are negative |
Subtopic: Spontaneity & Entropy | Gibbs Energy Change |
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Level 3: 35%-60%
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Consider the table given below and choose the correct option:
The effect of temperature on spontaneity can be represented by which of the following?
1. (B) and (D) only
2. (A) and (D) only
3. (B) and (C) only
4. (A) and (C) only
| ΔH | ΔS | Temperature | Spontaneity | |
| (A) | + | - | any T | Spontaneous |
| (B) | + | + | low T | Non spontaneous |
| (C) | - | - | low T | Spontaneous |
| (D) | - | + | any T | Non spontaneous |
The effect of temperature on spontaneity can be represented by which of the following?
1. (B) and (D) only
2. (A) and (D) only
3. (B) and (C) only
4. (A) and (C) only
Subtopic: Spontaneity & Entropy | Gibbs Energy Change |
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Level 1: 80%+
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Standard entropies of X2, Y2 and XY5 are 70, 50 and 110 JK–1mol–1 respectively. The temperature in Kelvin at which the given reaction will be at equilibrium is:
\(\frac{1}{2} \mathrm{X}_2+\frac{5}{2} \mathrm{Y}_2 \rightarrow \mathrm{XY}_5,~ \Delta \mathrm{H}=-35 \mathrm{~kJ} \mathrm{~mol}^{-1}\)
1. 300
2. 400
3. 600
4. 700
\(\frac{1}{2} \mathrm{X}_2+\frac{5}{2} \mathrm{Y}_2 \rightarrow \mathrm{XY}_5,~ \Delta \mathrm{H}=-35 \mathrm{~kJ} \mathrm{~mol}^{-1}\)
1. 300
2. 400
3. 600
4. 700
Subtopic: Thermodynamics' Properties and process | Spontaneity & Entropy | Gibbs Energy Change |
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Level 2: 60%+
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The standard enthalpy and entropy changes of decomposition of N2O4 to NO2 are 55.0 kJmol–1 and 175.0 JK–1 mol–1 respectively. The standard free energy change for this reaction at 25°C in J mol–1 is:
| 1. | 2750 | 2. | 2850 |
| 3. | 2875 | 4. | 2900 |
Subtopic: Spontaneity & Entropy | Gibbs Energy Change |
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Level 2: 60%+
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Which of the following statement is incorrect?
1. \(\triangle\text{G}=0\) for reversible process
2. \(\triangle\text{G}<0\) for spontaneous process
3. \(\triangle\text{G}>0\) for spontaneous process
4. \(\triangle\text{G}>0\) for non-spontaneous process
1. \(\triangle\text{G}=0\) for reversible process
2. \(\triangle\text{G}<0\) for spontaneous process
3. \(\triangle\text{G}>0\) for spontaneous process
4. \(\triangle\text{G}>0\) for non-spontaneous process
Subtopic: Gibbs Energy Change |
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For independent processes at 300 K.
\(\begin{array}{|c|c|c|} \hline \text { Process } & \Delta \mathbf{H} / \mathbf{k J} \mathrm{mol}^{-1} & \Delta \mathbf{S} / \mathrm{J} \mathrm{K}^{-1} \\ \hline \text { A } & -25 & -80 \\ \hline \text { B } & -22 & 40 \\ \hline \mathrm{C} & 25 & -50 \\ \hline \text { D } & 22 & 20 \\ \hline \end{array} \)
How many of the above process(es) are non-spontaneous?
1. 2 processes
2. 3 processes
3. 1 process
4. 4 process
\(\begin{array}{|c|c|c|} \hline \text { Process } & \Delta \mathbf{H} / \mathbf{k J} \mathrm{mol}^{-1} & \Delta \mathbf{S} / \mathrm{J} \mathrm{K}^{-1} \\ \hline \text { A } & -25 & -80 \\ \hline \text { B } & -22 & 40 \\ \hline \mathrm{C} & 25 & -50 \\ \hline \text { D } & 22 & 20 \\ \hline \end{array} \)
How many of the above process(es) are non-spontaneous?
1. 2 processes
2. 3 processes
3. 1 process
4. 4 process
Subtopic: Gibbs Energy Change |
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Identify correct match using Column I & Column II
| Column I | Column II | ||
| (i) | Spontaneous process | (a) | Isothermal and isobaric process |
| (ii) | \(\Delta H^\circ\) | (b) | \(\Delta H<0 \) |
| (iii) | \(\Delta T=0, \Delta P=0 \) | (c) | \(\Delta G<0 \) |
| (iv) | Exothermic process | (d) | (Bond energy of reactant) - (Bond energy of product) |
| I | II | III | IV | |
| 1. | c | d | a | b |
| 2. | b | a | c | d |
| 3. | d | b | c | d |
| 4. | a | d | b | c |
Subtopic: First Law of Thermodynamics | Spontaneity & Entropy | Gibbs Energy Change |
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Assuming ideal behaviour, for the reaction
3HC≡CH(g) ⇌ C₆H₆(l)
at 25°C, the magnitude of log K is expressed as x × 10⁻¹. Calculate the value of x.
Given:
ΔfG°(HC≡CH) = −2.04 × 10⁵ J mol⁻¹
ΔfG°(C₆H₆) = −1.24 × 10⁵ J mol⁻¹
R = 8.314 J K⁻¹ mol⁻¹
1. 860
2. 875
3. 855
4. 895
Subtopic: Gibbs Energy Change |
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Level 2: 60%+
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Calculate the minimum temperature at which the following reaction becomes spontaneous:
FeO(s) + C(graphite) → Fe(s) + CO(g)
Given:
ΔHf°(FeO) = –266.3 kJ mol⁻¹
ΔHf°(C) = 0
ΔHf°°(Fe) = 0
ΔHf°(CO) = –110.5 kJ mol⁻¹
ΔS°(FeO) = 57.49 J mol⁻¹ K⁻¹
ΔS°(C) = 5.74 J mol⁻¹ K⁻¹
ΔS°(Fe) = 27.28 J mol⁻¹ K⁻¹
ΔS°(CO) = 197.6 J mol⁻¹ K⁻¹
1. 365 K
2. 653 K
3. 1432 K
4. 964 K
Subtopic: Spontaneity & Entropy | Gibbs Energy Change |
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Consider the following cell reaction:
Cd(s) + Hg₂SO₄(s) + (9/5)H₂O(l) ⇌ CdSO₄·(9/5)H₂O(s) + 2Hg(l)
At 25°C, E°cell = 4.315 V and ΔH° = −825.2 kJ mol⁻¹
Calculate the standard entropy change, ΔS°, for the reaction.
Given: F = 96487 C mol⁻¹
1. 25.1 J K⁻¹mol-1
2. 29.1 J K⁻¹mol-1
3. 45.1 J K⁻¹mol-1
4. 67.6 J K⁻¹mol-1
Subtopic: Gibbs Energy Change |
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Level 2: 60%+
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