Chemical Equilibrium — Drills · Grade 11 Science

Chapter: Rates & Equilibrium

What these drills covers

By the end of Chemical Equilibrium you should be able to:

6 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: reversible reaction, dynamic equilibrium, Le Châtelier's principle, equilibrium shift, equilibrium constant (Keq), Haber process.

Problem 1

The double arrow (⇌) in a chemical equation shows that the reaction is…
  1. exothermic
  2. reversible
  3. already balanced
  4. complete
Answer and explanation

reversible

The ⇌ symbol means the reaction is reversible — it runs in both the forward and reverse directions at once.

Problem 2

At dynamic equilibrium, the concentrations of reactants and products…
  1. drop to zero
  2. keep rising
  3. are always equal
  4. stay constant
Answer and explanation

stay constant

At equilibrium the forward and reverse rates are equal, so the concentrations stay constant — though not necessarily equal.

Problem 3

For H₂(g) + I₂(g) ⇌ 2HI(g), an equilibrium mixture has [H₂] = 0.50 M, [I₂] = 0.50 M, and [HI] = 1.0 M. Calculate Keq.
Answer and explanation

4

Keq = [HI]² ÷ ([H₂][I₂]) = (1.0)² ÷ (0.50 × 0.50) = 1.0 ÷ 0.25 = 4.0.

Problem 4

Removing a product from a system at equilibrium as it forms will shift the equilibrium…
  1. toward the products
  2. so the reaction stops
  3. in no direction
  4. toward the reactants
Answer and explanation

toward the products

By Le Châtelier's principle, removing product makes the system shift toward the products to replace what was taken away.

Problem 5

A student claims that at equilibrium there must be equal amounts of reactants and products. Explain why this is wrong.
Answer and explanation

Equilibrium means the amounts stay constant, not that they are equal. The balance can lie far toward one side — a large Keq means mostly products and a small Keq means mostly reactants — while the forward and reverse rates remain equal.

Problem 6

For the exothermic reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g) + heat, which change would increase the equilibrium yield of NH₃?
  1. lowering the pressure
  2. increasing the pressure
  3. removing some N₂
  4. raising the temperature
Answer and explanation

increasing the pressure

The product side has fewer moles of gas (2 vs 4), so increasing the pressure shifts the equilibrium toward NH₃. Raising the temperature, lowering the pressure, or removing a reactant would all reduce the yield.

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