Questions on Equilibrium Constant (K_eq) and Calculations
Multiple-Choice Questions: Equilibrium Constant (K_eq) and Calculations
1. What does the equilibrium constant (K_eq) represent?
A) The rate of the forward reaction
B) The speed at which equilibrium is reached
C) The ratio of concentrations of products to reactants at equilibrium
D) The time required to reach equilibrium
E) The amount of catalyst used
2. Which of the following will appear in the K_eq expression?
A) Pure solids
B) Pure liquids
C) Aqueous ions
D) Solvent
E) Inert gases
3. In the reaction: H₂ + I₂ ⇌ 2HI, what is the K_eq expression?
A) [H₂][I₂]/[HI]²
B) [HI]/[H₂][I₂]
C) [HI]²/[H₂][I₂]
D) [H₂]/[HI][I₂]
E) [I₂]²/[HI]²
4. If K_eq = 1, what does that imply about the reaction at equilibrium?
A) Only products are present
B) Only reactants are present
C) Reactants and products are at equal concentrations
D) Forward reaction is faster
E) Reverse reaction is faster
5. For a reaction with K_eq = 4.5 × 10⁻⁷, the reaction favors:
A) Products strongly
B) Reactants strongly
C) Both equally
D) Neither reactants nor products
E) Cannot be determined
6. What is the unit of K_eq for the reaction: 2NO₂ ⇌ N₂O₄?
A) mol/L
B) (mol/L)²
C) No units
D) L/mol
E) Depends on the reaction stoichiometry
7. If K_eq = [products]/[reactants], then increasing the concentration of a product will:
A) Increase K_eq
B) Decrease K_eq
C) Have no effect on K_eq
D) Double K_eq
E) Invert K_eq
8. In the reaction: N₂ + 3H₂ ⇌ 2NH₃, what is the K_eq expression?
A) [N₂][H₂]³/[NH₃]²
B) [NH₃]²/[N₂][H₂]³
C) [NH₃]/[N₂][H₂]
D) [N₂]/[NH₃][H₂]
E) [H₂]³/[N₂][NH₃]²
9. If K_eq = 2.0 and the initial concentrations are: [A] = 1.0 M, [B] = 1.0 M, what is [C] at equilibrium for the reaction A + B ⇌ C?
A) 0.25 M
B) 0.5 M
C) 1.0 M
D) 2.0 M
E) Cannot determine without ICE table
10. What method is commonly used to calculate equilibrium concentrations?
A) Stoichiometry
B) ICE table
C) pH scale
D) Molarity conversion
E) Hess’s Law
11. When K_eq >> 1, the equilibrium lies:
A) Far to the left
B) Slightly to the left
C) In the middle
D) Far to the right
E) Toward both sides
12. A very small value of K_eq (e.g., 10⁻¹²) means:
A) The reaction goes to completion
B) Products dominate
C) Reactants dominate
D) The system is static
E) The temperature is high
13. Which changes the value of K_eq?
A) Adding a catalyst
B) Changing concentration
C) Changing pressure
D) Changing temperature
E) Dilution
14. If K_eq = 10 at 500 K and the temperature increases, what happens to K_eq for an exothermic reaction?
A) Increases
B) Decreases
C) Stays the same
D) Doubles
E) Becomes negative
15. What is the K_eq of a reaction reversed from its original direction?
A) Same as original
B) 1/K_eq
C) K_eq²
D) K_eq × 2
E) Negative of K_eq
16. In a reaction, doubling all coefficients affects K_eq how?
A) No change
B) Square K_eq
C) Halve K_eq
D) Invert K_eq
E) Multiply by number of species
17. If Q < K_eq, what will happen?
A) System is at equilibrium
B) Reaction shifts to form more products
C) Reaction shifts to form more reactants
D) No change
E) Reaction stops
18. What is Q (reaction quotient)?
A) The same as K_eq always
B) The rate of change of products
C) The ratio of product and reactant concentrations at any time
D) The time to reach equilibrium
E) The change in pressure
19. In the reaction: 2A ⇌ B, if K_eq = 4 and [A] = 1 M, what is [B]?
A) 0.5 M
B) 1 M
C) 2 M
D) 4 M
E) 0.25 M
20. What does a large K_eq value indicate?
A) Reaction is slow
B) Reaction has not started
C) Products are favored at equilibrium
D) Reactants are favored at equilibrium
E) The reaction is exothermic
Answer Key with Explanations
1. C – K_eq is the ratio of product concentrations to reactant concentrations at equilibrium.
2. C – Only aqueous and gaseous species appear in K_eq expressions.
3. C – K_eq = [HI]² / [H₂][I₂]
4. C – K_eq = 1 means equal concentrations of products and reactants at equilibrium.
5. B – A very small K_eq means the reaction favors reactants.
6. E – The unit of K_eq depends on the reaction stoichiometry (products minus reactants in mol).
7. C – K_eq is constant at a given temperature and is not affected by concentration changes.
8. B – K_eq = [NH₃]² / [N₂][H₂]³
9. B – Solving via ICE: x² / (1 - x)² = 2.0 → approximate value of 0.5 M.
10. B – The ICE table (Initial, Change, Equilibrium) is standard for equilibrium calculations.
11. D – If K_eq >> 1, products are favored and the equilibrium lies far to the right.
12. C – A very small K_eq indicates that reactants are dominant.
13. D – Temperature is the only factor that changes K_eq.
14. B – For exothermic reactions, increasing temperature shifts equilibrium left, decreasing K_eq.
15. B – Reversing a reaction gives a new K_eq equal to 1/K_eq.
16. B – Doubling coefficients squares the K_eq value.
17. B – Q < K_eq means system will shift toward products to reach equilibrium.
18. C – Q is the ratio of [products]/[reactants] at any given moment, not just at equilibrium.
19. C – K_eq = [B]/[A]² = x / (1²) = 4 → [B] = 4 M.
20. C – A large K_eq means products are highly favored at equilibrium.
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