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Unit 7: Equilibrium

Practice equilibrium concepts including K, Q, Le Châtelier’s Principle, and shifts in equilibrium.

Question 1

At equilibrium, the concentrations of reactants and products:

  1. are equal
  2. remain constant
  3. are zero
  4. are changing
Show answer

Correct answer: B

Why: At equilibrium, concentrations remain constant over time, but they are not necessarily equal.

Common mistake: Students think equilibrium means equal amounts.

Fix it: Equilibrium = constant, NOT equal

Question 2

If K > 1, the reaction favors:

  1. reactants
  2. products
  3. neither
  4. equilibrium shifts left
Show answer

Correct answer: B

Why: A large K means products are favored at equilibrium.

Common mistake: Confusing direction of shift.

Fix it: K > 1 → products dominate

Question 3

If Q < K, the reaction will:

  1. shift left
  2. shift right
  3. stay same
  4. stop
Show answer

Correct answer: B

Why: When Q < K, more products must form to reach equilibrium.

Common mistake: Mixing up Q vs K comparison.

Fix it: Q

Question 4

Adding more reactant will shift equilibrium:

  1. left
  2. right
  3. no change
  4. stop
Show answer

Correct answer: B

Why: System shifts to consume added reactant.

Common mistake: Forgetting Le Châtelier’s Principle.

Fix it: Add reactant → shift right

Question 5

Increasing temperature for an endothermic reaction shifts:

  1. left
  2. right
  3. no change
  4. depends on pressure
Show answer

Correct answer: B

Why: Heat acts like a reactant in endothermic reactions.

Common mistake: Not identifying reaction type.

Fix it: Endothermic → add heat → shift right

Question 6

A catalyst will:

  1. change K
  2. shift equilibrium
  3. speed up reaction
  4. increase products
Show answer

Correct answer: C

Why: Catalysts speed up both forward and reverse reactions equally.

Common mistake: Thinking catalyst changes equilibrium position.

Fix it: Catalyst = faster, not different

Question 7

Increasing pressure favors side with:

  1. more gas molecules
  2. fewer gas molecules
  3. no molecules
  4. liquids
Show answer

Correct answer: B

Why: System shifts to reduce pressure → fewer gas particles.

Common mistake: Forgetting gas count matters.

Fix it: High pressure → fewer moles side

Question 8

If K is very small, the reaction favors:

  1. products
  2. reactants
  3. equilibrium
  4. forward reaction
Show answer

Correct answer: B

Why: Small K means very little product is formed.

Common mistake: Confusing large vs small K.

Fix it: K

Question 9

Equilibrium is reached when:

  1. reaction stops
  2. forward = reverse rate
  3. products equal reactants
  4. no molecules move
Show answer

Correct answer: B

Why: Dynamic equilibrium means reactions continue but at equal rates.

Common mistake: Thinking reaction stops.

Fix it: Equilibrium = dynamic, not static

Question 10

Which change does NOT affect equilibrium?

  1. concentration
  2. pressure
  3. catalyst
  4. temperature
Show answer

Correct answer: C

Why: Catalysts do not change equilibrium position.

Common mistake: Thinking catalyst shifts reaction.

Fix it: Catalyst = speed only

Question 11

For the reaction:
N₂ + 3H₂ ⇌ 2NH₃

If pressure increases, equilibrium shifts:

  1. left
  2. right
  3. no change
  4. depends on temperature
Show answer

Correct answer: B

Why: Left side has 4 moles gas, right side has 2 → shift to fewer moles.

Common mistake: Not counting gas moles correctly.

Fix it: High pressure → fewer gas moles

Question 12

Which change will NOT shift equilibrium?

  1. adding reactant
  2. changing temperature
  3. adding catalyst
  4. removing product
Show answer

Correct answer: C

Why: Catalysts do not affect equilibrium position.

Common mistake: Thinking catalyst shifts equilibrium.

Fix it: Catalyst = speed only

Question 13

If K is very large, the reaction:

  1. favors reactants
  2. favors products
  3. does not occur
  4. is slow
Show answer

Correct answer: B

Why: Large K means products dominate.

Common mistake: Confusing rate with equilibrium.

Fix it: K = position, not speed

Question 14

If Q = K, the system:

  1. shifts right
  2. shifts left
  3. is at equilibrium
  4. stops
Show answer

Correct answer: C

Why: Q = K means equilibrium already reached.

Common mistake: Thinking reaction stops.

Fix it: Equilibrium = dynamic

Question 15

Which factor changes the value of K?

  1. concentration
  2. pressure
  3. catalyst
  4. temperature
Show answer

Correct answer: D

Why: Only temperature changes equilibrium constant.

Common mistake: Thinking pressure changes K.

Fix it: Only temp affects K

Question 16

Removing product causes equilibrium to:

  1. shift left
  2. shift right
  3. no change
  4. stop
Show answer

Correct answer: B

Why: System produces more product to replace removed amount.

Fix it: Remove product → shift right

Question 17

If a reaction is endothermic, increasing temperature will:

  1. decrease K
  2. increase K
  3. no change
  4. stop reaction
Show answer

Correct answer: B

Why: Heat is reactant → adding heat increases product formation → larger K.

Common mistake: Not connecting temp and K.

Fix it: Endothermic + heat → K increases

Question 18

Which expression is correct for equilibrium constant?

  1. reactants/products
  2. products/reactants
  3. sum of concentrations
  4. difference
Show answer

Correct answer: B

Why: K = products / reactants (each raised to coefficients).

Common mistake: Reversing fraction.

Fix it: Products on top

Question 19

Which species are NOT included in K expression?

  1. gases
  2. aqueous
  3. solids
  4. ions
Show answer

Correct answer: C

Why: Pure solids and liquids are omitted.

Common mistake: Including everything.

Fix it: Only (aq) and (g) count

Question 20

If volume decreases, pressure:

  1. decreases
  2. increases
  3. stays same
  4. becomes zero
Show answer

Correct answer: B

Why: Boyle’s Law: lower volume → higher pressure.

Common mistake: Forgetting inverse relationship.

Fix it: Volume ↓ → Pressure ↑

FRQ

Explain how a system at equilibrium responds to an increase in temperature for an endothermic reaction.

Show answer

Key points

  • heat is a reactant
  • system shifts right
  • more products formed

Sample answer: In an endothermic reaction, heat acts as a reactant. Increasing temperature adds more heat, causing the equilibrium to shift to the right to consume the added heat, resulting in more product formation.