Free NEET Chemistry multiple-choice questions on Gibbs Energy & Equilibrium. Attempt each question and reveal the answer with a full explanation.
The change in Gibbs free energy for a reaction is related to the EMF of the cell ( E cell ) by: G = -nFE cell G = nFE cell G = -RT E cell G = -E cell /nF A reaction is spontaneous at all temperatures if: H < 0 and S > 0 H > 0 and S < 0 H < 0 and S < 0 H > 0 and S > 0 Which of the following is a state function and also an extensive property? Enthalpy Heat Work Temperature The relation between G ⊖ and the equilibrium constant K is G ⊖ = -RT K . If K < 1 , then G ⊖ is: Positive Negative Zero Infinite At its boiling point, a liquid is in equilibrium with its vapor. The value of the Gibbs free energy change ( G ) for this phase transition is: Zero Positive Negative Infinity The unit of the gas constant R when used in the equation G = -RT K is: J , K -1 , mol -1 L , atm , K -1 , mol -1 cal , mol -1 m 3 , Pa , K -1 Which of the following is correct for a reversible process in a state of equilibrium? G = 0 S total < 0 G = 0 U = q For the process H 2O(s) H 2O(l) at 1 , atm and 273 , K , which of the following is true? G = 0 H = 0 S = 0 H < T S During the phase transition of ice to liquid water at 0 C and 1 , atm , which of the following is true? G = 0 H = 0 S = 0 V = 0 For an endothermic reaction, H is positive. Such a reaction is non-spontaneous at all temperatures if: S is negative S is positive S = 0 G is zero In a spontaneous process at constant temperature and pressure, the Gibbs free energy: Decreases Increases Remains constant Becomes zero A reaction has an equilibrium constant of 1.0 at 300 , K . The standard Gibbs free energy change G for this reaction is: 0 -RT RT 10 -1 , kJ , mol -1 A reaction occurs spontaneously if - T S > H and H is +ve and S are -ve T S = H and both H and S are +ve T S < H and both H and S are +ve T S > H and both H and S are +ve Which of the following pairs of a chemical reaction is certain to result in a spontaneous reaction - Endothermic and decreasing disorder Exothermic and increasing disorder Endothermic and increasing disorder Exothermic and decreasing disorder Identify the correct statement for change of Gibbs energy for a system ( G system ) at constant temperature and pressure:- If G system > 0 , the process is spontaneous If G system = 0 , the system has attained equilibrium If G system = 0 , the system is still moving in a particular direction If G system < 0 , the process is not spontaneous The enthalpy and entropy change for the reaction: Br2(l) + Cl2(g) -> 2BrCl(g) are 30 kJ mol -1 and 105 JK -1 mol -1 respectively. The temperature at which the reaction will be in equilibrium is:- 285.7K 273 K 450 K 300 K The correct thermodynamic conditions for the spontaneous reaction at all temperatures is H < 0 and S = 0 H > 0 and S < 0 H < 0 and S > 0 H < 0 and S < 0 For a reaction, H = 35.5 , kJ , mol -1 and S = 83.6 , J , K -1 , mol -1 . At what temperature is the reaction spontaneous? T > 425 , K T > 298 , K T < 425 , K T > 100 , K For the reaction Ag 2O(s) 2Ag(s) + 1 2 O 2(g) , the value of H is 30.56 , kJ , mol -1 and S is 66.0 , J , K -1 , mol -1 at 1 , atm . The temperature at which free energy change is zero is: 463 , K 300 , K 100 , K 553 , K The standard Gibbs free energy change G ∘ is related to the equilibrium constant K p by the expression: G ∘ = -RT K p G ∘ = RT K p G ∘ = -2.303 RT K p "Both A and C" The standard entropy of X 2, Y 2 and XY 3 are 60, 40 and 50 , J , K -1 , mol -1 respectively. For the reaction 1 2 X 2 + 3 2 Y 2 XY 3, H = -30 , kJ , to be at equilibrium, the temperature should be: 750 , K 1000 , K 1250 , K 500 , K What is the relationship between the heat of reaction at constant pressure ( q p ) and constant volume ( q v ) for the combustion of benzene C 6H 6(l) ? q p = q v - 1.5 RT q p = q v + 1.5 RT q p = q v - 3 RT q p = q v + 3 RT The variation of standard Gibbs free energy change with the equilibrium constant K is given by G = -RT K . If G > 0 , then the value of K is: Less than 1 Greater than 1 Zero Equal to 1 A reaction has H = -10 , kJ , mol -1 and S = -40 , J , K -1 , mol -1 . The reaction is spontaneous at: T < 250 , K T > 250 , K All temperatures No temperature For a reaction to be spontaneous at all temperatures, the conditions must be: ΔH < 0 and ΔS > 0 ΔH > 0 and ΔS < 0 ΔH < 0 and ΔS < 0 ΔH > 0 and ΔS > 0 For a reaction A + B ightarrow C + D , ΔH = -25 kJ and ΔS = -50 J K -1 . At what temperature will the reaction change from spontaneous to non-spontaneous? 500 K 250 K 300 K 1000 K A reaction A + B C is exothermic and has a negative entropy change. The reaction is: Spontaneous only at low temperatures Spontaneous only at high temperatures Spontaneous at all temperatures Non-spontaneous at all temperatures A reaction is exothermic and involves a decrease in entropy. Under what conditions will this reaction be spontaneous? At low temperatures At high temperatures At all temperatures It will never be spontaneous Compare the work done in a reversible isothermal expansion ( w rev ) and an irreversible isothermal expansion ( w irr ) of an ideal gas between the same initial and final volumes. Which is correct? |w rev | > |w irr | |w rev | < |w irr | |w rev | = |w irr | Work done is zero in both cases If the equilibrium constant for a reaction is 10 2 at 300 , K , the value of G is approximately ( R = 8.314 , J/K/mol ): -11.5 , kJ/mol -5.7 , kJ/mol +11.5 , kJ/mol -2.3 , kJ/mol The enthalpy of neutralization for the reaction of a strong acid ( HCl ) with a weak base ( NH 4OH ) is -51.4 , kJ , mol -1 . The enthalpy of ionization of NH 4OH is: +5.7 , kJ , mol -1 -5.7 , kJ , mol -1 +108.5 , kJ , mol -1 -108.5 , kJ , mol -1 For the reaction NH 4Cl(s) NH 3(g) + HCl(g) at 25 C , the enthalpy change H = 176 , kJ , mol -1 and entropy change S = 285 , J , K -1 , mol -1 . The reaction is: Non-spontaneous at 25 C Spontaneous at 25 C In equilibrium at 25 C Spontaneous only at very low temperatures The entropy change for the transition of liquid water to steam at 100 C is 109 , J , K -1 , mol -1 . What is the molar enthalpy of vaporization of water? 40.66 , kJ , mol -1 4.066 , kJ , mol -1 406.6 , kJ , mol -1 285.8 , kJ , mol -1 For a reaction to be spontaneous at all temperatures, the signs of H and S must be: H < 0, S > 0 H > 0, S < 0 H < 0, S < 0 H > 0, S > 0 For a reaction A(g) + 2B(g) C(g) , the value of S is negative. This reaction can be spontaneous only if: H is negative and | H| > |T S| H is positive and | H| < |T S| H is negative and | H| < |T S| The reaction is never spontaneous The heat of neutralization of LiOH and HCl at 25 C is -57.1 , kJ , mol -1 . The heat of neutralization of LiOH and CH 3COOH is likely to be: -55.2 , kJ , mol -1 -57.1 , kJ , mol -1 -60.5 , kJ , mol -1 -57.1 , J , mol -1 The criterion for spontaneity in terms of Helmholtz free energy ( A ) at constant volume and temperature is: A < 0 A > 0 A = 0 A is independent of spontaneity A reaction at 300 , K has H = 200 , kJ , mol -1 . To make the reaction spontaneous, the entropy change S must be: Greater than 666.7 , J , K -1 , mol -1 Less than 666.7 , J , K -1 , mol -1 Greater than 200 , J , K -1 , mol -1 Negative The property ( G P ) T for a substance is equal to: V -S H U The inversion temperature ( T i ) for a van der Waals gas is given by: 2a Rb a Rb a 2Rb 8a 27Rb In a reversible isothermal expansion of an ideal gas, the change in Gibbs free energy ( G ) is: nRT (P 2/P 1) nRT (V 2/V 1) Zero nRT (P 1/P 2) At constant temperature and pressure, a reaction will be non-spontaneous at all temperatures if: H > 0 and S < 0 H < 0 and S > 0 H > 0 and S > 0 H < 0 and S < 0 For a reaction to be spontaneous at high temperatures but non-spontaneous at low temperatures, the conditions must be: H > 0 and S > 0 H < 0 and S < 0 H > 0 and S < 0 H < 0 and S > 0 If G for a reaction is negative, the equilibrium constant K must be: K > 1 K < 1 K = 1 K = 0 A reaction occurs spontaneously if: T S > H and H is positive H < T S and both are positive T S = H and both are positive H > T S and both are positive Using Trouton's rule ( S vap 88 , J , K -1 , mol -1 ), the approximate boiling point of a liquid with an enthalpy of vaporization of 35.2 , kJ , mol -1 is: 400 , K 310 , K 250 , K 450 , K For which of the following gases will the Joule-Thomson expansion result in heating at room temperature? H 2 N 2 O 2 CO 2 The slope of the curve in a plot of K versus 1/T (Van't Hoff plot) is equal to: - H / R H / R S / R - G / RT If the equilibrium constant for a reaction is 10 at 300 , K , the standard Gibbs free energy change ( G ) is: ( R = 8.314 , J , K -1 , mol -1 ) -5.74 , kJ , mol -1 -5.74 , J , mol -1 +5.74 , kJ , mol -1 -2.49 , kJ , mol -1 The intensive property among the following is: Standard electrode potential ( E ) Gibbs free energy ( G ) Entropy ( S ) Enthalpy ( H ) Using the Gibbs energy change, G = + 63.3 kJ , for the following reaction, Ag2CO3 <=> 2Ag+ (aq) + CO3 2- (aq) the K sp of Ag2CO3(s) in water at 25 C is :- ( R = 8.314 J K -1 mol -1 ) 3.2 10 -26 8.0 10 -12 2.9 10 -3 7.9 10 -2 For the reaction : X2O4(l) -> 2XO2(g) U = 2.1 k cal , S = 20 cal K -1 at 300 K Hence G is :- 2.7 k cal - 2.7 k cal 9.3 k cal - 9.3 k cal Under isothermal and reversible conditions, the term "free energy" in thermodynamics signifies Expansion work done on the system Non-expansion work done by the system Expansion work done by the system Non-expansion work done on the system Hydrolysis of sucrose is given by the following reaction. Sucrose + H 2 O Glucose + Fructose If the equilibrium constant ( K c ) is 2 10 13 at 300 K, the value of r G at the same temperature will be : 8.314 J mol -1 K -1 300 K (2 10 13 ) 8.314 J mol -1 K -1 300 K (3 10 13 ) -8.314 J mol -1 K -1 300 K (4 10 13 ) -8.314 J mol -1 K -1 300 K (2 10 13 ) The equilibrium concentrations of the species in the reaction A + B C + D are 2, 3, 10 and 6 mol L -1 , respectively at 300 K. G for the reaction is (R = 2 cal/mol K) 1372.60 cal −137.26 cal −1381.80 cal −13.73 cal If G for a reaction is zero, then the equilibrium constant K is: 1 0 10 Consider the following reaction : 2 A ( g ) + B ( g ) 2 D ( g ) U = -10 kJ mol -1 and S = -44 JK -1 at 298 K. Identify the correct option with G for the reaction and spontaneity of the reaction at 298 K. (Given : R = 8.31 J mol -1 K -1 ) +0.63568 kJ mol -1 , non-spontaneous -0.63568 kJ mol -1 , spontaneous -1.635 kJ mol -1 , spontaneous +1.635 kJ mol -1 , non-spontaneous For the reaction X 2O 4(l) ightarrow 2XO 2(g) at 300 K , ΔU = 2.1 kcal and ΔS = 20 cal K -1 . What is the value of ΔG for the reaction? -2.7 kcal +2.7 kcal 0.9 kcal -0.9 kcal The relation ΔG = ΔG ⊖ + RT ln Q helps in determining spontaneity. If Q < K , then: ΔG < 0 , reaction proceeds forward ΔG > 0 , reaction proceeds backward ΔG = 0 , reaction is at equilibrium ΔG < 0 , reaction proceeds backward The criterion for the spontaneity of a process at constant T and V is: A < 0 G < 0 S < 0 H < 0 The heat of combustion of CH 4(g) at constant volume is measured in a bomb calorimeter at 298 , K and is found to be -885.4 , kJ , mol -1 . The value of enthalpy of combustion is: -890.3 , kJ , mol -1 -885.4 , kJ , mol -1 -880.5 , kJ , mol -1 -900.2 , kJ , mol -1 During the Joule-Thomson expansion of a real gas above its inversion temperature, the gas will: Show a heating effect Show a cooling effect Show no temperature change Liquefy immediately The Gibbs-Helmholtz equation relates the change in Gibbs free energy with temperature. It is expressed as: ( ( G/T) T ) P = - H T 2 G = H + T S G = V P - S T ( G T ) P = S Which of the following is the correct Gibbs-Helmholtz equation in terms of enthalpy ( H ) and temperature ( T )? ( (G/T)/ T) P = -H/T 2 ( (G/T)/ T) P = H/T 2 ( G/ T) P = H/T G = H + T S For a reaction where H = -110 kJ/mol and S = -40 J/K/mol , what is the temperature above which the reaction becomes non-spontaneous? 2750 K 275 K 4400 K 440 K Which of the following thermodynamic relations is derived from the definition of Gibbs free energy G = H - TS and H = U + PV ? dG = VdP - SdT dG = VdP + SdT dG = -VdP + SdT dG = PdV - SdT Identify the correct condition for a spontaneous process in a closed system at constant temperature and pressure: G < 0 S sys > 0 G > 0 S surr > 0 Which of the following is a criterion for spontaneity in terms of the Helmholtz free energy ( A )? (dA) T,V 0 (dA) T,P 0 (dA) S,V 0 (dA) S,P 0 A protein undergoes reversible thermal denaturation from its initial state N to denatured state D according to N <=> D . At 60ºC, the concentrations of both N and D are equal at equilibrium, and the standard enthalpy change of denaturation is 666 kJ mol -1 . The standard entropy change ( S° in kJ K -1 mol -1 ) of the protein upon denaturation at 60ºC is closest to 2.0 2000.0 333.0 11.1 Which of the following is a criterion for equilibrium? (ΔG) T,P = 0 (ΔS) system = 0 (ΔU) V,S > 0 (ΔH) P,S < 0 A process is in equilibrium. The correct statement is: G = 0 S = 0 H = 0 G ∘ = 0