Free NEET Physics multiple-choice questions on Second Law & Entropy. Attempt each question and reveal the answer with a full explanation.
Which of the following processes is accompanied by an increase in entropy? Sublimation of dry ice Condensation of steam Freezing of water Polishing a mirror Which of the following is the standard state of Carbon? Graphite Diamond Buckminsterfullerene Coal Calculate the change in entropy when 2 moles of an ideal gas are heated from 300 K to 600 K at constant pressure. (Given: C p = 5 2 R and 2 = 0.693 ) 28.8 J/K 11.5 J/K 5.76 J/K 14.4 J/K For which of the following substances is the molar entropy expected to be non-zero even at 0 K ? CO Pure Diamond Pure Ice (monocrystalline) Solid Argon The change in Gibbs free energy ( G ) for a reaction at constant temperature is related to the reaction quotient ( Q ) by: G = G + RT Q G = G - RT Q G = RT (Q/K) G = RT Q A Carnot engine whose sink is at 300 K has an efficiency of 40%. By how much should the temperature of source be increased so as to increase its efficiency by 50% of original efficiency:- 275 K 325 K 250 K 380 K An engine has an efficiency of 1/6. When the temperature of sink is reduced by 62°C, its efficiency is doubled. Temperature of the source is 37°C 62°C 99°C 124°C A refrigerator works between 4 C and 30 C. It is required to remove 600 calories of heat every second in order to keep the temperature of the refrigerated space constant. The power required is: (Take 1 cal = 4.2 Joules) 2.365 W 23.65 W 236.5 W 2365 W Bond dissociation enthalpies of H 2(g) , Cl 2(g) and HCl(g) are 434 , 242 and 431 kJ mol -1 respectively. Enthalpy of formation of HCl(g) is: -93 kJ mol -1 -245 kJ mol -1 +93 kJ mol -1 +245 kJ mol -1 The bond energy of C-H bond in methane from the following data: C(s) + 2H 2(g) CH 4(g) H = -74.8 kJ ; H sublimation of C(s) = 716.7 kJ ; BE(H-H) = 435.9 kJ . 415.9 kJ/mol 1663.5 kJ/mol 350.2 kJ/mol 831.7 kJ/mol For the reaction: 2A(g) + B(g) 2D(g) , U = -10.5 kJ and S = -44.1 J K -1 . Calculate G for the reaction at 298 K . -0.16 kJ +0.16 kJ -12.9 kJ +12.9 kJ The standard enthalpy of combustion at 25 C of H 2(g) , C(s) and C 2H 6(g) are -285.8 , -393.5 and -1560.0 kJ mol -1 respectively. The standard enthalpy of formation of C 2H 6(g) is: -84.6 kJ mol -1 +84.6 kJ mol -1 -100.2 kJ mol -1 +156.0 kJ mol -1 For a spontaneous process, which of the following is always true? ( S system + S surroundings ) > 0 S system > 0 S surroundings > 0 H < 0 The enthalpy change for the reaction N 2(g) + 3H 2(g) 2NH 3(g) is -92.2 kJ . If the bond energies of N N and H-H are 945 and 436 kJ/mol respectively, what is the bond energy of N-H ? 391 kJ/mol 1173 kJ/mol 350 kJ/mol 460 kJ/mol Calculate the standard enthalpy of reaction for: H 2(g) + 1 2 O 2(g) H 2O(g) . Given bond energies: H-H = 436 kJ/mol , O=O = 498 kJ/mol , O-H = 464 kJ/mol . -243 kJ/mol -486 kJ/mol +243 kJ/mol -121.5 kJ/mol The bond dissociation energies of X 2 , Y 2 and XY are in the ratio of 1:0.5:1 . H for the formation of XY is -200 kJ mol -1 . The bond dissociation energy of X 2 will be: 800 kJ mol -1 200 kJ mol -1 100 kJ mol -1 400 kJ mol -1 The bond enthalpy of H 2 , X 2 and HX are in the ratio 2:1:2 . If H f for HX is -100 kJ/mol , the bond enthalpy of X 2 is: 200 kJ/mol 100 kJ/mol 300 kJ/mol 400 kJ/mol A sample of an ideal gas undergoes an isothermal expansion from volume V 1 to V 2 in a reversible manner. The entropy change of the surroundings is: -nR (V 2/V 1) nR (V 2/V 1) Zero nRT (V 2/V 1) The standard enthalpy of formation of CO 2(g) , H 2O(l) and CH 4(g) are -393.5 , -285.8 and -74.8 kJ mol -1 respectively. The enthalpy of combustion of methane is: -890.3 kJ mol -1 +890.3 kJ mol -1 -604.5 kJ mol -1 +604.5 kJ mol -1 Trouton's rule states that the entropy of vaporization for most liquids (that do not have hydrogen bonding) is approximately: 88 J K -1 mol -1 0 J K -1 mol -1 110 J K -1 mol -1 44 J K -1 mol -1 The Clausius-Clapeyron equation relates the vapor pressure of a substance to its: Temperature and Enthalpy of vaporization Volume and Entropy Pressure and Internal energy Temperature and Density The entropy change for the surroundings when 1 mole of water is formed from its elements under standard conditions ( H f = -286 kJ/mol ) at 298 K is: 959.7 J K -1 mol -1 -959.7 J K -1 mol -1 0.96 J K -1 mol -1 -286 J K -1 mol -1 Calculate the change in enthalpy ( H ) for the reaction: C 2H 4(g) + H 2(g) C 2H 6(g) . Given bond enthalpies: C=C is 615 kJ/mol , C-C is 348 kJ/mol , H-H is 435 kJ/mol , and C-H is 414 kJ/mol . -125 kJ/mol +125 kJ/mol -250 kJ/mol +250 kJ/mol In a reaction, H and S are both positive. The reaction will be spontaneous at: High temperatures Low temperatures All temperatures No temperatures The enthalpy of hydrogenation of cyclohexene is -119.5 kJ mol -1 . If the enthalpy of hydrogenation of benzene is -208.1 kJ mol -1 , the resonance energy of benzene is: -150.4 kJ mol -1 -358.5 kJ mol -1 -119.5 kJ mol -1 -208.1 kJ mol -1 Given that the bond energies of O=O is 498 kJ/mol and the enthalpy of formation of O 3(g) is 142 kJ/mol , calculate the average bond energy of the O-O bond in O 3 . 302 kJ/mol 142 kJ/mol 200 kJ/mol 498 kJ/mol Which relationship correctly represents the Gibbs-Helmholtz equation? G = H + T[ ( G)/ T] P G = H - T[ ( G)/ T] P H = G - T[ ( G)/ T] P G = H + [ ( G)/ T] P For an ideal gas undergoing an isothermal process, the change in Helmholtz free energy ( A ) is equal to: The work done in a reversible process The heat exchanged The change in internal energy The change in enthalpy The molar entropy of mixing for two ideal gases when n 1 moles of gas 1 and n 2 moles of gas 2 are mixed at constant temperature and pressure is given by: S mix = -R(n 1 x 1 + n 2 x 2) S mix = R(n 1 x 1 + n 2 x 2) S mix = -RT(n 1 x 1 + n 2 x 2) S mix = n 1 R V 1 + n 2 R V 2 Which of the following describes the Clausius-Clapeyron equation in differential form for a liquid-vapor equilibrium? dP/dT = L / (T V) dP/dT = T V / L dV/dT = L / (P T) dP/dV = L / (T 2) In a reversible adiabatic process, the relationship between P and T is given by: P 1- T = constant PT = constant P T = constant P T 1- = constant Calculate the entropy of mixing when 1 mole of Oxygen gas and 1 mole of Nitrogen gas are mixed at constant temperature and pressure, assuming ideal behavior. 2R 2 R 2 -2R 2 Zero Which relation between thermodynamic potentials is a correct Maxwell relation? ( T V ) S = -( P S ) V ( T P ) S = ( V S ) P ( S V ) T = ( P T ) V All of these Which of the following is an exact differential? dU q w dq + dw Which of the following is an intensive property? Density Mass Volume Enthalpy What is the entropy change ( S ) for the surroundings when 1 mole of an ideal gas expands isothermally and reversibly at 300 K ? -nR (V 2/V 1) nR (V 2/V 1) Zero Infinite Which Maxwell relation is derived from the Gibbs free energy definition G = H - TS ? ( V/ T) P = -( S/ P) T ( T/ V) S = -( P/ S) V ( T/ P) S = ( V/ S) P ( S/ V) T = ( P/ T) V According to the Third Law of Thermodynamics, which substance has zero entropy at 0 K? Perfectly crystalline solid Amorphous solid Supercooled liquid Any element in gaseous state For which of the following reactions is S positive? MgCO 3(s) MgO(s) + CO 2(g) H 2O(l) H 2O(s) 2SO 2(g) + O 2(g) 2SO 3(g) N 2(g) + 3H 2(g) 2NH 3(g) Which of the following describes the Clausius statement of the Second Law of Thermodynamics? Heat cannot flow from a colder body to a hotter body without external work. The entropy of the universe always increases in a spontaneous process. No engine can be 100% efficient. The total energy of the universe is constant. For a reaction to be spontaneous at all temperatures: H < 0, S > 0 H > 0, S < 0 H < 0, S < 0 H > 0, S > 0 What is the entropy change (in J K -1 mol -1 ) for the conversion of ice at 0 C to water at 0 C ? (Given: Enthalpy of fusion of ice = 6.025 kJ/mol ) 22.07 2.207 220.7 20.27 In a reversible adiabatic process, the entropy change is: Zero Positive Negative Infinite The Boltzmann constant k B relates entropy S and thermodynamic probability W by the equation: S = k B W S = k B W S = k B W S = W k B The standard entropy of formation of O 3(g) is not zero because: Oxygen in its standard state is O 2(g) , not O 3(g) 平衡 Entropy is always positive for all substances Ozone is a gas Ozone is an allotrope of oxygen Which of the following is an extensive property? Gibbs Free Energy Density Temperature Molar heat capacity For a reversible process at equilibrium, the change in Gibbs free energy ( G ) is: 0 Negative Positive Infinite Which statement best describes the Second Law of Thermodynamics regarding heat engines? It is impossible to construct a heat engine that converts all heat absorbed from a reservoir into work. Heat can flow from a colder body to a hotter body without external work. Energy cannot be created or destroyed. Entropy of a system always decreases in a spontaneous process. The value of S is negative for which of the following processes? Condensation of water vapor Melting of ice Dissolution of sugar in water Sublimation of iodine What is the relation between K p and G ? G = -RT K p G = RT K p K p = e G / RT G = -2.303 RT K p The entropy of vaporization of a liquid is 110 J K -1 mol -1 and its enthalpy of vaporization is 44 kJ mol -1 . The boiling point of the liquid is: 400 K 400 C 250 K 4.4 K Which of the following is true for a spontaneous process in an isolated system? S > 0 S < 0 G > 0 H < 0 Which of the following is a criterion for equilibrium in terms of entropy? S total = 0 S sys = 0 S surr = 0 S total > 0 For a reaction to be spontaneous at all temperatures, the correct condition is: H < 0 and S > 0 H > 0 and S < 0 H < 0 and S < 0 H > 0 and S > 0 The unit of entropy is: J K -1 mol -1 J mol -1 J K mol J -1 K -1 mol -1 Which of the following describes an 'isolated system'? No exchange of mass or energy with surroundings Exchange of energy but no mass with surroundings Exchange of mass but no energy with surroundings Exchange of both mass and energy with surroundings The entropy of mixing for two ideal gases is always: Positive Negative Zero Dependent on the nature of the gases What is the relation between the change in Gibbs free energy ( G ) and the cell potential ( E ) of an electrochemical cell? G = -nFE G = nFE G = -nRT E G = -F/E For a monoatomic gas undergoing an adiabatic process, the relation between Pressure ( P ) and Volume ( V ) is PV x = constant . What is x ? 5/3 7/5 1.4 1 The molar entropy of a substance is highest in which state? Gaseous state Liquid state Solid state Perfectly crystalline state The intensive property among the following is: Molar heat capacity Heat capacity Enthalpy Entropy During an isothermal expansion of an ideal gas, the entropy of the system: Increases Decreases Remains constant Becomes zero Which of the following statements is a consequence of the Second Law of Thermodynamics? Heat cannot flow by itself from a colder body to a hotter body. Energy is conserved in all natural processes. The total internal energy of an isolated system is constant. Temperature is a measure of average kinetic energy. Which of the following is an extensive property? Entropy Temperature Viscosity Surface tension In a reversible process, the entropy of the universe: Remains constant Increases Decreases Becomes zero For a reaction to be in equilibrium, the total entropy of the universe ( Δ S total ) must be: Zero Maximum Minimum Positive According to the Third Law of Thermodynamics, the entropy of a perfectly crystalline substance at absolute zero ( 0 K ) is: Zero Maximum Minimum but not zero Infinite For an adiabatic process, the relation between volume V and temperature T is: T V -1 = constant T V = constant T V = constant T V 1- = constant For which of the following is the standard molar entropy ( S ) at 298 K expected to be the highest? H 2O(g) H 2O(l) H 2O(s) All have the same entropy A reaction is at equilibrium. If H = 30.5 kJ mol -1 and S = 0.06 kJ K -1 mol -1 , the temperature at equilibrium is: 508.3 K 450.5 K 300.2 K 100.8 K Identify the intensive property among the following options. Refractive Index Enthalpy Entropy Gibbs Free Energy The change in entropy ( dS ) is defined as: dQ rev /T (dQ + dW)/T (dU + dW)/T None of these For the reaction S(s) + O 2(g) SO 2(g) , which of the following is correct? H = U H > U H < U H = 0 An ideal gas heat engine operates in Carnot cycle between 227 C and 127 C . It absorbs 6 10 4 cals of heat at higher temperature. Amount of heat converted to work is:- 4.8 10 4 cals 2.4 10 4 cals 1.2 10 4 cals 6 10 4 cals The efficiency of an ideal heat engine working between the freezing point and boiling point of water, is 6.25% 20% 26.8% 12.5% A Carnot engine has an efficiency of 50% when its source is at a temperature 327°C. The temperature of the sink is 27°C 15°C 100°C 200°C The entropy change of the universe during an irreversible process is: Always greater than zero Always zero Always less than zero Constant Under which of the following conditions is a process spontaneous at all temperatures? H < 0 and S > 0 H > 0 and S < 0 H < 0 and S < 0 H > 0 and S > 0 The entropy change ( S ) for the fusion of 1 mole of ice at 273 K (heat of fusion of ice is 6.0 kJ/mol ) is: 21.98 J K -1 mol -1 10.50 J K -1 mol -1 31.20 J K -1 mol -1 273 J K -1 mol -1 In a closed flask, the transition Ice Water is in equilibrium. What happens to the equilibrium if the pressure is increased? More ice melts More water freezes No change occurs Temperature increases If the enthalpy change for the transition of liquid water to steam is 30 kJ mol -1 at 27 C , the entropy change for the process would be: 100 J mol -1 K -1 10 J mol -1 K -1 1.0 J mol -1 K -1 0.1 J mol -1 K -1 What is the change in entropy when 1 mole of an ideal gas expands isothermally and reversibly from 10 L to 100 L ? 19.14 J K -1 2.303 J K -1 8.314 J K -1 38.28 J K -1 A reaction at 1 bar and 298 K has H = 200 kJ mol -1 and S = 100 J K -1 mol -1 . At what temperature range will the reaction be spontaneous? Above 2000 K Below 2000 K Above 200 K Below 200 K The entropy change for the reversible isothermal expansion of an ideal gas is given by: S = nR (V 2/V 1) S = nR (P 2/P 1) S = C v (T 2/T 1) S = 0 For which of the following processes is S negative? N 2(g) + 3H 2(g) 2NH 3(g) CaCO 3(s) CaO(s) + CO 2(g) H 2(g) 2H(g) Zn(s) + CuSO 4(aq) ZnSO 4(aq) + Cu(s) The equilibrium constant for a reaction is 10 . What will be the value of G ∘ ? ( R = 8.314 J K -1 mol -1 , T = 300 K ) -5.74 kJ mol -1 -57.4 kJ mol -1 +5.74 kJ mol -1 -0.574 kJ mol -1 The entropy change for the expansion of an ideal gas from volume V 1 to V 2 at constant temperature is: nR (V 2/V 1) nR (V 1/V 2) nC v (V 2/V 1) nC p (V 2/V 1) For a spontaneous process, the total entropy change of the universe (system + surroundings) must be: Greater than zero Equal to zero Less than zero Constant Which of the following substances has a non-zero entropy even at absolute zero ( 0 K ), violating the simplest form of the Third Law of Thermodynamics? CO Diamond Ice Pure crystalline Ag For a reaction to be spontaneous at all temperatures, the values of enthalpy and entropy must satisfy: H < 0, S > 0 H > 0, S < 0 H < 0, S < 0 H > 0, S > 0 One mole of an ideal gas at 300 K is expanded isothermally from an initial pressure of 10 atm to 1 atm . The G for this process is: -5744 J 5744 J -11488 J 0 J A reaction has a negative enthalpy change and a negative entropy change. This reaction will be spontaneous at: Low temperatures High temperatures All temperatures No temperatures Which of the following is the correct mathematical expression for the Second Law of Thermodynamics regarding the entropy of the universe? S total = S system + S surrounding > 0 for irreversible processes S total = S system + S surrounding = 0 for irreversible processes S system > 0 for all spontaneous processes S surrounding > 0 for all spontaneous processes A reaction has a standard enthalpy change of H = -100 kJ and a standard entropy change of S = -200 J K -1 . At what temperature will the reaction reach equilibrium? 500 K 200 K 1000 K 0.5 K A certain reaction is non-spontaneous at low temperature but becomes spontaneous at high temperature. This implies: H is positive and S is positive H is negative and S is negative H is positive and S is negative H is negative and S is positive The heat of formation of an element in its standard state is zero. In which case is this NOT applicable for carbon? Diamond Graphite Neither, both are zero Both are non-zero The temperature T at which the reaction Ag 2O(s) 2Ag(s) + 1/2 O 2(g) is at equilibrium is (Given H = 30.5 kJ/mol and S = 0.066 kJ/K mol ): 462.1 K 30.5 K 100 K 196 K If the entropy change for a reaction is S = -100 J K -1 and the enthalpy change is H = -30 kJ , at what temperature will the reaction become non-spontaneous? Above 300 K Below 300 K At all temperatures Never For a reaction to occur spontaneously at all temperatures, the values of H and S must be: H < 0, S > 0 H > 0, S < 0 H < 0, S < 0 H > 0, S > 0 The heat of formation of H 2O(l) is -286 kJ/mol . The entropy change of the surroundings at 25 C is: 959.7 J/K -959.7 J/K 286 J/K -286 J/K Which of the following conditions is necessary for a process to be reversible? The process must be quasi-static and dissipative forces must be absent. The process must be fast. The system must be in an isolated container. The internal energy must remain constant. The enthalpy of neutralization of HF by NaOH is approximately -68.3 kJ/mol , which is higher than the standard -57.3 kJ/mol . This is because: The hydration energy of the fluoride ion is very high HF is a very strong acid The H-F bond energy is very low Fluorine is the most electronegative element Which of the following substances has a non-zero residual entropy at 0 K due to structural disorder? CO Ne Diamond NaCl Which of the following is an intensive property that describes the ability of a system to do electrical work? Electromotive force (EMF) Internal energy Gibbs free energy Entropy The entropy change for the surroundings when a system undergoes an endothermic process is: Always negative Always positive Zero Dependent on the pressure The change in Gibbs free energy ( G ) for the expansion of 2 moles of an ideal gas from 10 atm to 1 atm at 300 K is: -11.48 kJ 11.48 kJ -5.74 kJ 5.74 kJ The maximum work obtainable from a system at constant temperature and pressure is given by the decrease in: Gibbs free energy ( G ) Helmholtz free energy ( A ) Internal energy ( U ) Enthalpy ( H ) In the Born-Haber cycle for the formation of NaCl(s) , which of the following steps is always exothermic? Electron gain enthalpy of Cl Sublimation of Na Ionization of Na Dissociation of Cl 2 What is the entropy change when 1 mole of an ideal gas is heated from 300 K to 600 K at constant volume? ( C v = 3/2 R ) 3/2 R 2 3/2 R (1/2) 5/2 R 2 R 2 For the reaction 2Cl(g) Cl 2(g) , the signs of H and S are respectively: Negative, Negative Positive, Positive Negative, Positive Positive, Negative For the combustion of ethane ( C 2H 6 ), n g is: -0.5 -1.5 0.5 1 Which of the following describes the 'Clausius inequality' for any real process? dQ/T 0 dQ/T > 0 dQ/T = 0 S sys < 0 A reaction has H = -100 kJ and S = -200 J/K . Above what temperature does the reaction become non-spontaneous? 500 K 200 K 1000 K 250 K Which of the following substances possesses residual entropy at 0 K due to the random orientation of molecules in the crystal lattice? N 2O Solid CO 2 Solid Ar Solid O 2 For the reaction X 2O 4(l) 2XO 2(g) , U = 2.1 kcal and S = 20 cal K -1 at 300 K . What is G for the reaction? -2.7 kcal +2.7 kcal -9.3 kcal +9.3 kcal The lattice enthalpy and enthalpy of solution of NaCl are 788 kJ mol -1 and 4 kJ mol -1 respectively. The enthalpy of hydration of NaCl is: -784 kJ mol -1 +784 kJ mol -1 -792 kJ mol -1 +792 kJ mol -1 For which reaction is the standard entropy of reaction ( S ) expected to be negative? 2H 2(g) + O 2(g) 2H 2O(l) MgCO 3(s) MgO(s) + CO 2(g) H 2(g) + Cl 2(g) 2HCl(g) C 6H 12 O 6(s) + 6O 2(g) 6CO 2(g) + 6H 2O(g) The heat of neutralization of HCl by NaOH is -57.1 kJ . When 1 mole of CH 3COOH is neutralized by 1 mole of NaOH , the heat evolved is 55.2 kJ . The heat of dissociation of CH 3COOH is: 1.9 kJ -1.9 kJ 112.3 kJ -112.3 kJ What is the entropy change for the isothermal expansion of 1 mole of an ideal gas from V to 10V ? ( R = 8.314 J K -1 mol -1 ) 19.14 J K -1 2.303 J K -1 8.314 J K -1 38.28 J K -1 For an endothermic reaction where H > 0 , the reaction can be spontaneous only if: S > H/T S < H/T S = 0 S < 0 In which case is the entropy change negative? Liquid water freezing to ice Sublimation of solid iodine Dissolution of salt in water Expansion of a gas at constant temperature In a spontaneous process, the entropy of the system: May increase or decrease Must increase Must decrease Remains constant Which of the following conditions represents a system at equilibrium? G = 0 at constant T and P S total = 0 Both A and B H = 0 Which of the following is the criteria for spontaneity of a process at constant temperature and volume? Δ A < 0 Δ G < 0 Δ S sys > 0 Δ H < 0 When 100 J of heat is transferred from a reservoir at 400 K to another at 300 K , the net change in entropy of the universe is: +0.083 J/K -0.083 J/K +0.25 J/K Zero The standard Gibbs free energy change ( Δ G ∘ ) for the cell reaction Zn(s) + Cu 2+ (aq) Zn 2+ (aq) + Cu(s) is calculated using E ∘ cell = 1.10 V . The value (in kJ) is: -212.3 kJ -106.1 kJ +212.3 kJ -424.6 kJ The standard enthalpy of atomization of CH 3Cl(g) is 1570 kJ/mol . If the average bond enthalpy of C-H is 412 kJ/mol , the bond enthalpy of C-Cl is: 334 kJ/mol 1158 kJ/mol 746 kJ/mol 412 kJ/mol According to Trouton's Rule, the entropy of vaporization for many non-polar liquids at their normal boiling point is approximately: 88 J K -1 mol -1 0 J K -1 mol -1 25 J K -1 mol -1 150 J K -1 mol -1 Standard molar entropy of H 2(g) is 130.6 J K -1 mol -1 . Is the entropy of an element in its standard state zero? No, only for perfectly crystalline substances at 0 K Yes, by convention Yes, for all elements Only for monatomic gases Which of the following processes is non-spontaneous at all temperatures? Endothermic with decrease in entropy Exothermic with increase in entropy Endothermic with increase in entropy Exothermic with decrease in entropy When 1 mole of an ideal gas is heated from 298 K to 596 K at constant pressure, the entropy change is: C p 2 C v 2 R 2 2 C p