This set of Chemistry Multiple Choice Questions and Answers for Class 11 focuses on “Relationship between Equilibrium Constant K, Reaction Quotient Q and Gibbs Energy G”.

1. In a reaction, at 300k, K_{C} is given as 2 x 10^{13}, then what is the value of ΔG?

a) – 7.64 × 10^{4} J

b) – 7.64 × 10^{4} J mol^{–1}

c) – 7.64 × 10 J mol^{–1}

d) – 7.64 × 10^{4} mol^{–1}

View Answer

Explanation: We know that ΔG

_{0}= – RT lnK

_{c}, where ΔG

_{0}is the standard Gibbs free energy, R is universal gas constant, T is the temperature and K

_{C}is equilibrium constant; substituting K

_{C}as 2 x 10

^{13}, ΔG

_{0}= (– 8.314J mol

^{–1}K

^{–1}× 300K) × ln(2×10

^{13}); ΔG

_{0}= – 7.64 × 10

^{4}J mol

^{–1}.

2. For a chemical reaction, the value of ΔG_{0} is -831.4 J/mol. Then what is the value of K_{C} at 100 k?

a) 1.0077

b) 1.077

c) 1.007

d) 2.7

View Answer

Explanation: We know that ΔG

_{0}= – RT lnK

_{c}, where ΔG

_{0}is the standard Gibbs free energy, R is universal gas constant, T is the temperature and K

_{C}is equilibrium constant; substituting ΔG

_{0}as -831.4 J/mol, we get lnk = -831.4J/mol divided by -8.314J mol

^{–1}K

^{–1}× 100K = 1; lnk = 1; K = e

^{1}= 2.7

3. If the value of ΔG_{0} is -2502 J/mol and K is 2, what is the temperature of the reaction that is occurring?

a) 200 k

b) 101 k

c) 100 k

d) 300 k

View Answer

Explanation: We know that ΔG

_{0}= – RT lnK

_{c}, where ΔG

_{0}is the standard Gibbs free energy, R is universal gas constant, T is the temperature and K

_{C}is equilibrium constant; substituting ΔG

_{0}as -2502 J/mol, we get -2502 J/mol = -8.314J mol

^{–1}K

^{–1}× T ln2 = 2502 J/mol = T = 2502/2.502 = 100 k.

4. In a reaction, if the value of Gibbs free energy is greater than zero what does it infer?

a) K is greater than 1

b) K is less than 1

c) K is equal to 1

d) Cannot deduce K from Gibbs free energy

View Answer

Explanation: If the value of Gibbs free energy is greater than the zero that means, -ΔG

_{0}/RT is negative and that e

^{-ΔG0/RT}is greater than 1, so the K is greater than 1 this means the reaction is nonspontaneous and proceeds in the forward direction.

5. When is a reaction nonspontaneous?

a) Gibbs free energy is positive

b) Gibbs free energy is negative

c) Gibbs free energy is zero

d) Does not depend on Gibbs free energy

View Answer

Explanation: When Gibbs free energy is positive, the reaction that occurs is nonspontaneous and a reaction occurs backward that is the products are converted into reactants. Simply the reverse reaction could occur.

6. What did the Q depicted in the equation; ΔG = ΔG_{0} + RT lnQ?

a) reaction coefficient

b) reaction quotient

c) equilibrium constant

d) free energy

View Answer

Explanation: In the equation ΔG = ΔG

_{0}+ RT lnQ, ΔG is the Gibbs free energy, R is the universal gas constant, T is the temperature and Q is the reaction quotient. When Gibbs free energy is zero, the reaction quotient becomes equilibrium constant.

7. If the value of Gibbs free energy for a reaction is 20J/mol, the reaction is ___________

a) spontaneous

b) nonspontaneous

c) may be spontaneous

d) may not be spontaneous

View Answer

Explanation: Is the value of Gibbs free energy for a reaction is 20 J/mol, that means it is positive, -ΔG

_{0}/RT is negative and that e

^{-ΔG0/RT}is greater than 1, so the K is greater than 1 this means the reaction is nonspontaneous.

8. For a reaction, K_{c} = 3.81 × 10^{–3} and ΔG_{0} = 13.8 kJ/mol. Then what is the value of R?

a) -8.314J mol^{–1}K^{–1}

b) 8.314J mol^{–1}K^{–1}

c) cannot say as the temperature is not given

d) -8.314J mol^{–1}

View Answer

Explanation: Though the temperature is not given, universal gas constant value always remains the same, whatever may be the other values. So the universal gas constant is given by a constant value that is -8.314J mol

^{–1}K

^{–1}.

9. What happens when reaction quotient is equal to the equilibrium constant?

a) the reaction proceeds in the forward direction

b) the reaction proceeds in the backward direction

c) the reaction reaches equilibrium

d) cannot predict

View Answer

Explanation: When Gibbs free energy is zero, the reaction reaches equilibrium and at equilibrium, the reaction quotient is replaced by the equilibrium constant, as both the values are equal. That is when reaction quotient is equal to the equilibrium constant reaction reaches equilibrium.

10. Is a relationship between reaction quotient and Gibbs free energy at a temperature T?

a) ΔG = ΔG_{0} + RT lnQ

b) ΔG = ΔG_{0} + RT lnk

c) ΔG = ΔG_{0} + R lnQ

d) ΔD = ΔG_{0} + RT lnQ

View Answer

Explanation: The relationship between reaction quotient and Gibbs free energy at temperature t is given as as ΔG = ΔG

_{0}+ RT lnQ, where ΔG is the Gibbs free energy, R is the universal gas constant, T is the temperature and Q is the reaction quotient.

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