Which mixing of 1 M acid and 1 M base produces maximum rise in temperature?
A50 mL HCl + 20 mL NaOH
B30 mL HCl + 30 mL NaOH
C45 mL CH₃COOH + 25 mL NaOH
D30 mL CH₃COOH + 30 mL NaOH
✅ Correct: B
Max heat is produced when moles of acid = moles of base (complete neutralisation). 30 mL×1 M HCl + 30 mL×1 M NaOH → 0.03 mol each, complete neutralisation, max heat. Option D gives incomplete neutralisation (CH₃COOH is weak). \(\mathbf{30\text{ mL HCl} + 30\text{ mL NaOH}}\).
Q2
A liquid is stirred mechanically in a thermally insulated vessel. Which statement is correct?
AΔU = 0, q < 0, w > 0
BΔU > 0, q = 0, w > 0
CΔU = 0, q = 0, w = 0
DΔU < 0, q = 0, w > 0
✅ Correct: B
Thermally insulated: \(q = 0\). Work is done on the liquid by stirring: \(w > 0\) (work done on system is positive). By first law: \(\Delta U = q + w = 0 + w > 0\). Internal energy increases (temperature rises). \(\mathbf{\Delta U > 0, q = 0, w > 0}\).
Q3
For a reaction with ΔH > 0 and ΔS > 0, the reaction is spontaneous when:
ATemperature is high
BTemperature is low
CAt any temperature
DReaction is never spontaneous
✅ Correct: A
\(\Delta G = \Delta H - T\Delta S\). For \(\Delta H > 0, \Delta S > 0\): \(\Delta G\) is negative (spontaneous) only when \(T\Delta S > \Delta H\), i.e., at high temperature. At low temperature, \(\Delta G > 0\) (non-spontaneous).
Q4
For which process is ΔH = ΔU?
AH₂(g) + Cl₂(g) → 2HCl(g)
BN₂(g) + 3H₂(g) → 2NH₃(g)
CC(s) + O₂(g) → CO₂(g)
DCaCO₃(s) → CaO(s) + CO₂(g)
✅ Correct: A
\(\Delta H = \Delta U + \Delta n_g RT\). \(\Delta H = \Delta U\) when \(\Delta n_g = 0\). For H₂ + Cl₂ → 2HCl: \(\Delta n_g = 2-(1+1) = 0\). \(\mathbf{\Delta H = \Delta U}\) for this reaction.
Q5
The heat of combustion of carbon to CO₂ is −393.5 kJ/mol and to CO is −110.5 kJ/mol. The heat of combustion of CO to CO₂ is:
A−393.5 kJ
B−283 kJ
C+283 kJ
D−504 kJ
✅ Correct: B
Using Hess's law: C + O₂ → CO₂, ΔH = −393.5 kJ. C + ½O₂ → CO, ΔH = −110.5 kJ. Subtracting: CO + ½O₂ → CO₂, ΔH = −393.5 − (−110.5) = \(\mathbf{-283\text{ kJ}}\).
Q6
Bond dissociation energy of H₂ is 436 kJ/mol and that of HCl is 431 kJ/mol. Enthalpy of formation of HCl from H₂ and Cl₂ is −92 kJ/mol. Bond energy of Cl₂ is:
Entropy of the universe (system + surroundings) in a spontaneous process:
ADecreases
BRemains constant
CIncreases
DMay increase or decrease
✅ Correct: C
Second law of thermodynamics: entropy of the universe always increases in a spontaneous process. \(\Delta S_{universe} = \Delta S_{system} + \Delta S_{surroundings} > 0\). For reversible process: \(\Delta S_{universe} = 0\). For irreversible (spontaneous): \(\Delta S_{universe} > 0\).
Q8
The standard Gibbs energy change for a reaction at 298 K is −20 kJ/mol. The equilibrium constant K for this reaction is approximately: (R = 8.314 J/mol·K)
Which of the following has the highest standard entropy (S°)?
AH₂(g)
BCO₂(g)
CDiamond (s)
DNaCl(s)
✅ Correct: B
Entropy is higher for: gases > liquids > solids, and larger/more complex molecules. CO₂(g) has highest entropy among options — it is a gas and has more atoms (3) than H₂ (2). Diamond has very low entropy (rigid crystal). \(\mathbf{CO_2(g)}\).
Q10
For a reversible adiabatic expansion, which relationship is correct?
ATV^(γ-1) = constant
BPV = constant
CTV = constant
DPV^γ = constant
✅ Correct: D
For reversible adiabatic process: \(PV^\gamma = \text{constant}\) (Poisson's equation). Also: \(TV^{\gamma-1} = \text{const}\) and \(TP^{(1-\gamma)/\gamma} = \text{const}\). The most fundamental and directly tested form is \(\mathbf{PV^\gamma = \text{const}}\).
Q11
The enthalpy of vaporisation of water is 40.7 kJ/mol at 100°C. The entropy change during vaporisation is approximately:
A109 J/mol·K
B407 J/mol·K
C40.7 J/mol·K
D0.407 J/mol·K
✅ Correct: A
\(\Delta S = \Delta H_{vap}/T = 40700\text{ J/mol}/(373\text{ K}) = \mathbf{109\text{ J/mol·K}}\). This is Trouton's rule value (~88 J/mol·K for most liquids; water is higher due to H-bonding).
Q12
Which of the following processes has negative entropy change (ΔS < 0)?
ASublimation of dry ice
BDissolution of KNO₃ in water
CCrystallisation of sugar from solution
DMelting of ice
✅ Correct: C
Crystallisation reduces disorder — molecules go from random solution to ordered crystal lattice. ΔS < 0. All other processes (sublimation, dissolution, melting) increase disorder → ΔS > 0.
Q13
The heat of formation of CO₂ is the heat of reaction for:
ACO + ½O₂ → CO₂
B2C + 2O₂ → 2CO₂
CC(graphite) + O₂(g) → CO₂(g)
DC(diamond) + O₂(g) → CO₂(g)
✅ Correct: C
Standard heat of formation is the enthalpy change when 1 mole of compound is formed from elements in their standard states. Standard state of C is graphite (not diamond). \(\mathbf{C(\text{graphite}) + O_2(g) \to CO_2(g)}\).
Q14
At constant pressure, the heat evolved in a reaction is the change in:
AInternal energy (ΔU)
BEnthalpy (ΔH)
CGibbs energy (ΔG)
DEntropy (ΔS)
✅ Correct: B
At constant pressure: \(q_p = \Delta H\). This is the enthalpy change. At constant volume: \(q_v = \Delta U\). Most reactions occur at constant atmospheric pressure, so calorimetric measurements give \(\mathbf{\Delta H}\).
Q15
The relationship between Kp and Kc for the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g) is:
Lattice energy of NaCl is −788 kJ/mol and hydration energy is −774 kJ/mol. The heat of solution of NaCl is:
A−1562 kJ/mol
B+14 kJ/mol
C−14 kJ/mol
D+1562 kJ/mol
✅ Correct: B
\(\Delta H_{solution} = \Delta H_{lattice}(+) + \Delta H_{hydration} = +788 + (-774) = \mathbf{+14\text{ kJ/mol}}\). Positive heat of solution means NaCl dissolves endothermically. But the dissolution is still spontaneous due to large entropy increase.
Q17
For the reaction: 2H₂O(l) → 2H₂(g) + O₂(g), ΔH = +572 kJ. The enthalpy of formation of H₂O(l) is:
A−286 kJ/mol
B+286 kJ/mol
C−572 kJ/mol
D+572 kJ/mol
✅ Correct: A
The reverse reaction: H₂(g) + ½O₂(g) → H₂O(l) has ΔH = −572/2 = \(\mathbf{-286\text{ kJ/mol}}\). The enthalpy of formation of H₂O(l) is −286 kJ/mol (formation from elements in standard states).
Q18
Which of the following is an extensive property?
ATemperature
BPressure
CEnthalpy
DMolar heat capacity
✅ Correct: C
Extensive properties depend on the amount of substance: enthalpy (H), internal energy (U), entropy (S), volume (V), mass. Intensive properties are independent of amount: temperature, pressure, molar quantities, density, molar heat capacity.
Q19
The combustion of 1 mole of methane (CH₄) releases 890 kJ of heat at constant pressure. The enthalpy of combustion of methane is:
A+890 kJ/mol
B−890 kJ/mol
C−445 kJ/mol
D+445 kJ/mol
✅ Correct: B
Combustion releases heat → exothermic → ΔH is negative. ΔH_combustion of CH₄ = \(\mathbf{-890\text{ kJ/mol}}\). The negative sign indicates heat is released to surroundings (exothermic process).
Q20
A reaction is endothermic (ΔH > 0) and the entropy decreases (ΔS < 0). This reaction is:
ASpontaneous at high temperature
BSpontaneous at low temperature
CNever spontaneous under any conditions
DAlways spontaneous
✅ Correct: C
\(\Delta G = \Delta H - T\Delta S\). With \(\Delta H > 0\) and \(\Delta S < 0\): \(-T\Delta S > 0\), so \(\Delta G = (+) + (+) > 0\) at ALL temperatures. \(\mathbf{\text{Never spontaneous}}\) under any conditions.
R
Roshan
Expert · 5 Years Experience
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