The occurrence of a reaction is impossible if [AIIMS 1982, 91; MP PET 1997; MP PMT 1999; DPMT 2002]

(1) ΔH is +ve ; ΔS is also + ve but ΔH < TΔS

(2) ΔH is – ve ; ΔS is also – ve but ΔH > TΔS

(3) ΔH is – ve ; ΔS is + ve

(4) ΔH is + ve ; ΔS is – ve

Concept Questions :-

Spontaneity and Entropy
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When enthalpy and entropy change for a chemical reaction are –2.5 × 103 cal and 7.4 cal deg–1 respectively. Predict the reaction at 298 K is [AFMC 1998; MH CET 1999; CBSE PMT 2000]

(1) Spontaneous

(2) Reversible

(3) Irreversible

(4) Non-spontaneous

Concept Questions :-

Gibbs Energy Change
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Which of the following is true for the reaction H2O(l)H2O(g) at 100°C and 1 atmosphere [KCET 1991; AIIMS 1996]

(1) ΔE = 0

(2) ΔH = 0

(3) ΔH = ΔE

(4) ΔH = TΔS

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The enthalpy of vapourization water is 386 kJ. What is the entropy of water [BHU 1997]

(1) 0.5 kJ

(2) 1.03 kJ

(3) 1.5 kJ

(4) 22.05 kJ

Concept Questions :-

Spontaneity and Entropy
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Identify the correct statement regarding entropy [CBSE PMT 1998; BHU 2001]

(1) At 0°C, the entropy of a perfectly crystalline substance is taken to be zero

(2) At absolute zero of temperature, the entropy of a perfectly crystalline substance is +ve

(3) At absolute zero of temperature, the entropy of all crystalline substances is taken to be zero

(4) At absolute zero of temperature, the entropy of a perfectly crystalline substance is taken to be zero

Concept Questions :-

Spontaneity and Entropy
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An engine operating between 150°C and 25°C takes 500 J heat from a higher temperature reservoir if there are no frictional losses, then work done by engine is [MH CET 1999]

(1) 147.7 J

(2) 157.75 J

(3) 165.85 J

(4) 169.95 J

Concept Questions :-

First Law of Thermodynamics
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The standard entropies of CO2(g), C(s) and O2(g) are 213.5, 5.690 and 205 JK–1 respectively. The standard entropy of formation of CO2(g) is [CPMT 2001]

(1) 1.86 JK–1

(2) 1.96 JK–1

(3) 2.81 JK–1

(4) 2.86 JK–1

Concept Questions :-

Thermochemistry
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Equal volumes of monoatomic and diatomic gases at same initial temperature and pressure are mixed. The ratio of specific heats of the mixture (Cp/Cv) will be [AFMC 2002]

(1) 1

(2) 2

(3) 1.67

(4) 1.5

Concept Questions :-

CP and CV and Relation for Real Gas
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The unit of entropy is [CBSE PMT 2002]

(1) J mol–1

(2) JK mol–1

(3) J mol–1 K–1

(4) J–1 K–1 mol–1

Concept Questions :-

Spontaneity and Entropy
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The entropy changed involved in the conversion of 1 mole of liquid water at 373 K to vapour at the same temperature will be [ΔHvap=2.257kJ/gm] [MP PET 2002]

(1) 0.119 kJ

(2) 0.109 kJ

(3) 0.129 kJ

(4) 0.120 kJ

Concept Questions :-

Spontaneity and Entropy
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