Chemistry Questions and Answers – Relationship between Equilibrium Constant K, Reaction Quotient Q and Gibbs Energy G

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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, KC is given as 2 x 1013, then what is the value of ΔG?
a) – 7.64 × 104 J
b) – 7.64 × 104 J mol–1
c) – 7.64 × 10 J mol–1
d) – 7.64 × 104 mol–1

Explanation: We know that ΔG0 = – RT lnKc, where ΔG0 is the standard Gibbs free energy, R is universal gas constant, T is the temperature and KC is equilibrium constant; substituting KC as 2 x 1013, ΔG0 = (– 8.314J mol–1K–1 × 300K) × ln(2×1013); ΔG0 = – 7.64 × 104 J mol–1.

2. For a chemical reaction, the value of ΔG0 is -831.4 J/mol. Then what is the value of KC at 100 k?
a) 1.0077
b) 1.077
c) 1.007
d) 2.7

Explanation: We know that ΔG0 = – RT lnKc, where ΔG0 is the standard Gibbs free energy, R is universal gas constant, T is the temperature and KC is equilibrium constant; substituting ΔG0 as -831.4 J/mol, we get lnk = -831.4J/mol divided by -8.314J mol–1K–1 × 100K = 1; lnk = 1; K = e1 = 2.7

3. If the value of ΔG0 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

Explanation: We know that ΔG0 = – RT lnKc, where ΔG0 is the standard Gibbs free energy, R is universal gas constant, T is the temperature and KC is equilibrium constant; substituting ΔG0 as -2502 J/mol, we get -2502 J/mol = -8.314J mol–1K–1 × T ln2 = 2502 J/mol = T = 2502/2.502 = 100 k.
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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

Explanation: If the value of Gibbs free energy is greater than the zero that means, -ΔG0/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

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 = ΔG0 + RT lnQ?
a) reaction coefficient
b) reaction quotient
c) equilibrium constant
d) free energy

Explanation: In the equation ΔG = ΔG0 + 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

Explanation: Is the value of Gibbs free energy for a reaction is 20 J/mol, that means it is positive, -ΔG0/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, Kc = 3.81 × 10–3 and ΔG0 = 13.8 kJ/mol. Then what is the value of R?
a) -8.314J mol–1K–1
b) 8.314J mol–1K–1
c) cannot say as the temperature is not given
d) -8.314J mol–1

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–1K–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

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 = ΔG0 + RT lnQ
b) ΔG = ΔG0 + RT lnk
c) ΔG = ΔG0 + R lnQ
d) ΔD = ΔG0 + RT lnQ

Explanation: The relationship between reaction quotient and Gibbs free energy at temperature t is given as as ΔG = ΔG0 + 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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