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Chemistry 30

Chemistry 30 · Worksheets

Equilibrium

Ten questions of mixed difficulty, covering Equilibrium. Print it, or work through it on screen — the answer key starts on its own page.

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Equilibrium

Chemistry 30 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

  1. For the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g), the equilibrium constant expression is

    1. a) ([N₂][H₂]³) ÷ [NH₃]²
    2. b) 2[NH₃] ÷ ([N₂] × 3[H₂])
    3. c) [NH₃]² ÷ ([N₂] + [H₂]³)
    4. d) [NH₃]² ÷ ([N₂][H₂]³)

  2. For an exothermic forward reaction, raising the temperature

    1. a) shifts the equilibrium right and increases K
    2. b) shifts the equilibrium left and decreases K
    3. c) shifts the equilibrium left and increases K
    4. d) has no effect on K

  3. Adding an inert gas such as argon to a gaseous equilibrium at constant volume

    1. a) shifts the equilibrium toward the products
    2. b) shifts the equilibrium toward fewer moles of gas
    3. c) increases K
    4. d) causes no shift, because the concentrations of the reacting gases are unchanged

  4. 1.00 mol of H₂ and 1.00 mol of I₂ are placed in a 1.00 L container. At equilibrium, [HI] = 1.56 mol/L. The value of K for H₂(g) + I₂(g) ⇌ 2HI(g) is closest to

    1. a) 0.02
    2. b) 50
    3. c) 7.1
    4. d) 2.4

  5. Adding a catalyst to a system at equilibrium

    1. a) shifts the equilibrium toward the products
    2. b) increases the value of K
    3. c) does not shift the equilibrium, but it is reached sooner
    4. d) shifts the equilibrium toward the reactants

  6. Adding more reactant to a system at equilibrium causes the equilibrium to shift

    1. a) not at all, since K is constant
    2. b) toward whichever side has fewer moles
    3. c) toward the products, using up some of the added reactant
    4. d) toward the reactants

  7. Chemical equilibrium can only be reached in

    1. a) an open beaker
    2. b) a system with a catalyst
    3. c) a system at 0 °C
    4. d) a closed system

  8. At equilibrium, the forward and reverse reactions

    1. a) occur one after the other
    2. b) proceed at equal rates
    3. c) have equal concentrations
    4. d) have both stopped

  9. A reaction with K = 1 × 10⁶ at equilibrium

    1. a) strongly favours the reactants
    2. b) cannot reach equilibrium
    3. c) strongly favours the products
    4. d) has equal amounts of reactants and products

  10. For N₂(g) + 3H₂(g) ⇌ 2NH₃(g), increasing the pressure by reducing the volume shifts the equilibrium

    1. a) neither way, since pressure does not affect equilibrium
    2. b) right, toward the side with fewer moles of gas
    3. c) left, because ammonia is a gas
    4. d) left, toward the side with more moles of gas

Answer key · Equilibrium

Chemistry 30 · maddyhelps.com

  1. d) [NH₃]² ÷ ([N₂][H₂]³) — Products over reactants, each concentration raised to the power of its coefficient. Coefficients become exponents, never multipliers.
  2. b) shifts the equilibrium left and decreases K — Treat heat as a product of an exothermic reaction: adding heat pushes the system back toward reactants. Temperature is the only change that actually alters the value of K.
  3. d) causes no shift, because the concentrations of the reacting gases are unchanged — Total pressure rises, but the partial pressures and concentrations of the species in the equilibrium expression do not change, so there is nothing for the system to respond to. Pressure only matters when it is caused by a volume change.
  4. b) 50 — An ICE table: 1.56 mol/L of HI forms, and HI comes 2 for every 1 of each reactant, so 0.78 mol/L of each is used, leaving 0.22 mol/L. K = (1.56)² ÷ (0.22)(0.22) = 2.43 ÷ 0.0484 ≈ 50.
  5. c) does not shift the equilibrium, but it is reached sooner — A catalyst speeds the forward and reverse reactions equally, so the position of equilibrium is untouched. It changes how fast you get there, not where you end up.
  6. c) toward the products, using up some of the added reactant — Le Chatelier's principle: the system partly undoes the change imposed on it. K itself does not change — only the concentrations adjust until the ratio matches K again.
  7. d) a closed system — If products can escape — a gas leaving an open container, for example — the reverse reaction never gets the chance to keep up, so the system never settles.
  8. b) proceed at equal rates — Equilibrium is dynamic: both reactions keep going, but at the same rate, so nothing appears to change. Equal rates is not the same as equal concentrations.
  9. c) strongly favours the products — K is products over reactants, so a very large K means the numerator dominates — at equilibrium the mixture is almost all product. A very small K means almost all reactant.
  10. b) right, toward the side with fewer moles of gas — Four moles of gas on the left, two on the right. Squeezing the system favours the side that relieves the pressure by occupying fewer moles — the right. If both sides had equal moles of gas, pressure would have no effect.