Unit 7 Practice: Medium
Equilibrium · 20 questions. Try each question before revealing the answer and worked explanation.
Question 1
Write Kc for:
N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
Show answer and explanation
Answer:
Kc = [NH₃]² / ([N₂][H₂]³)
Explanation: Each concentration is raised to its stoichiometric coefficient.
Question 2
Write Kc for:
CaCO₃(s) ⇌ CaO(s) + CO₂(g)
Show answer and explanation
Answer:
Kc = [CO₂]
Explanation: CaCO₃ and CaO are pure solids, so they are omitted.
Only CO₂ appears.
Question 3
For a reaction, K = 25. What does this suggest?
Show answer and explanation
Answer: Products are favored.
Explanation: Because K is greater than 1, equilibrium lies more toward products.
It does not mean the reaction goes 100% to completion.
Question 4
For a reaction, K = 2.0 × 10⁻⁶. What does this suggest?
Show answer and explanation
Answer: Reactants are strongly favored.
Explanation: The very small value means only a relatively small amount of product exists at equilibrium.
Question 5
A reaction has K = 4.0. What is K for the reverse reaction?
Show answer and explanation
Answer: 0.25
Work:
Kreverse = 1/4.0 = 0.25
Question 6
A reaction has K = 3.0. What is K if the entire equation is doubled?
Show answer and explanation
Answer: 9.0
Work:
Knew = K²
= 3.0²
= 9.0
Question 7
Reaction 1 has K₁ = 2.0 and Reaction 2 has K₂ = 5.0. If the reactions are added, what is Koverall?
Show answer and explanation
Answer: 10
Work:
Koverall = K₁K₂
= 2.0 × 5.0
= 10
Question 8
For:
A ⇌ B
K = 4.0.
At some moment:
[A] = 0.50 M [B] = 1.00 M
Find Q and predict the shift.
Show answer and explanation
Answer: Q = 2.0, so the reaction shifts right.
Work:
Q = [B]/[A]
= 1.00/0.50
= 2.0
Since:
Q < K
the reaction moves toward products.
Question 9
For the same reaction, K = 4.0.
If:
[A] = 0.20 M [B] = 1.20 M
predict the shift.
Show answer and explanation
Answer: Left
Work:
Q = 1.20/0.20
= 6.0
Since:
Q > K
the reaction shifts toward reactants.
Question 10
For:
A ⇌ B
initially:
[A] = 1.00 M [B] = 0
At equilibrium:
[B] = 0.40 M
Find equilibrium [A].
Show answer and explanation
Answer: 0.60 M
Explanation: For every 1 mol B formed, 1 mol A is consumed.
A decreases by 0.40 M:
1.00 − 0.40 = 0.60 M
Question 11
Using Question 10, calculate Kc.
Show answer and explanation
Answer: 0.667
Work:
Kc = [B]/[A]
= 0.40/0.60
= 0.667
Question 12
For:
A ⇌ 2B
initially:
[A] = 1.00 M [B] = 0
If x M of A reacts, what are the equilibrium concentrations?
Show answer and explanation
Answer:
[A]eq = 1.00 − x
[B]eq = 2x
Explanation: The balanced equation shows that every 1 mole of A produces 2 moles of B.
Question 13
For:
N₂ + 3H₂ ⇌ 2NH₃
What happens if NH₃ is added?
Show answer and explanation
Answer: The equilibrium shifts left.
Explanation: Adding product creates excess product.
The system responds by consuming some NH₃ and forming reactants.
Question 14
For the same reaction, what happens if H₂ is removed?
Show answer and explanation
Answer: The equilibrium shifts left.
Explanation: Removing a reactant causes the system to shift toward the side that replaces it.
Question 15
For:
N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
What happens if the container volume decreases?
Show answer and explanation
Answer: The equilibrium shifts right.
Explanation: Decreasing volume increases pressure.
The left side has:
4 moles gas
The right has:
2 moles gas
The system shifts toward fewer gas particles.
Question 16
For:
H₂(g) + I₂(g) ⇌ 2HI(g)
What happens if volume decreases?
Show answer and explanation
Answer: No significant shift.
Explanation: There are 2 total moles of gas on each side.
Changing volume affects both sides equally in the ideal model.
Question 17
What happens if an inert gas is added at constant volume?
Show answer and explanation
Answer: No equilibrium shift.
Explanation: The partial pressures of the reacting gases do not change when volume and temperature remain constant.
The total pressure increases, but equilibrium depends on the reacting species.
Question 18
For an exothermic reaction:
Reactants ⇌ Products + heat
what happens if temperature increases?
Show answer and explanation
Answer: The equilibrium shifts left.
Explanation: Adding heat is similar to adding a product.
The system shifts toward reactants to consume some of the added heat.
Question 19
For an endothermic reaction:
Reactants + heat ⇌ Products
what happens if temperature increases?
Show answer and explanation
Answer: The equilibrium shifts right.
Explanation: Heat acts like a reactant.
Adding heat favors the direction that consumes it.
Question 20
Write Ksp for:
AgCl(s) ⇌ Ag⁺(aq) + Cl⁻(aq)
Show answer and explanation
Answer:
Ksp = [Ag⁺][Cl⁻]
Explanation: The solid is omitted from the equilibrium expression.