Chemical Thermodynamics MCQs Question and Answer in Engineering Chemistry

1

Standard entropy of crystalline carbon monoxide (in kJ/mol) at 0 K is around

A) 0.03 B) 2.50 C) zero D) 5.76

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Answer & Solution

Answer: Option D

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2

For an irreversible adiabatic expansion of a perfect gas from volume V_i to V_f, the change in entropy of the gas is

A) nR In(V_f/V_i) B) zero C) less than zero D) greater than zero

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Answer & Solution

Answer: Option D

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3

The change in entropy when two moles of argon gas are heated at constant volume from 300 K to 500 K is

A) -12.74 J/K/mol B) -6.37 J/K/mol C) 6.37 J/K/mol D) 12.74 J/K/mol

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Answer & Solution

Answer: Option D

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4

For the reaction, N₂(g) + 3H₂(g) → 2NH₃(g)
compute the entropy change (in J/K/mol) for the process and comment on the sign of the property.

Data

Species
S°(J/K/mol)

NH₃(g)
192.3

N₂(g)
191.5

H₂(g)
130.6

A) ΔS° = -37.65 J/K/mol; negative sign indicates that there is a decrease in the gaseous species during the reaction B) ΔS° = -198.7 J/K/mol; negative sign indicates that there is a decrease in the gaseous species during the reaction C) ΔS° = -31.25 J/K/mol; negative sign indicates that there is a decrease in the gaseous species during the reaction D) ΔS° = +31.25 J/K/mol; positive sign indicates that the reaction is spontaneous

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Answer & Solution

Answer: Option B

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5

Given that standard molar enthalpies of formation of NO(g) and NO₂(g) are respectively 90.3 kJ/mol and 33.2 kJ/mol, the enthalpy change for the reaction 2NO(g) + O₂(g) → 2NO₂(g) is

A) 16.6 kJ B) -57.1 kJ C) -114.2 kJ D) 57.1 kJ

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Answer & Solution

Answer: Option C

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6

The standard free energies of formation of H₂S(g) and CdS(s) at 1000°C are -49.0 kJ/mol and -127.2 kJ/mol respectively. Use these data to predict whether H₂(g) will reduce CdS(s) to metallic Cd at this temperature.

A) ΔG = -78.2 kJ/mol and H₂ reduces CdS B) ΔG = -39.1 kJ/mol and H₂ reduces CdS C) ΔG = 0 kJ/mol and the reaction is at equilibrium D) ΔG = 78.2 kJ/mol and the reaction is not feasible

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Answer & Solution

Answer: Option D

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7

For the reaction, 2Cl(g) → Cl₂(g) the thermodynamic properties

A) ΔG, ΔH and ΔS are positive B) ΔG, ΔH and ΔS are negative C) ΔG, ΔH are negative and ΔS is positive D) ΔG is negative and ΔH, ΔS are positive

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Answer & Solution

Answer: Option B

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8

According to conventional transition state theory, for elementary bimolecular reactions, the molar entropy of activation ΔS^± is

A) positive B) zero C) negative D) positive for endothermic and negative for exothermic reactions

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Answer & Solution

Answer: Option C

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9

The enthalpy of formation of AgCl is obtained from the enthalpy change from which one of the following process?

A) Ag⁺(aq) + Cl^-(aq) → AgCl(s) B) Ag(s) + $$\frac{1}{2}$$Cl₂(g) → AgCl(s) C) AgCl(s) → Ag(s) + $$\frac{1}{2}$$Cl₂(g) D) Ag(s) + AuCl → Au(s) + AgCl(s)

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Answer & Solution

Answer: Option B

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10

For the process, 1Ar(300 K, 1 bar) → 1Ar(200 K, 10 bar) assuming ideal gas behaviour, the change in molar entropy is

A) -27.57 J/K/mol B) +27.57 J/K/mol C) -24.20 J/K/mol D) +24.20 J/K/mol

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Answer & Solution

Answer: Option A

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