Rates & Equilibrium — Chapter quiz · Physical Science: Chemistry, Grade 11

Distinguish reaction speed from equilibrium composition and calculate direction of adjustment.

Problem 1

Which change will speed up a chemical reaction?
  1. decreasing the concentration of a reactant
  2. increasing the surface area of a solid reactant
  3. adding an inhibitor
  4. lowering the temperature
Answer and explanation

increasing the surface area of a solid reactant

Greater surface area exposes more particles, allowing more effective collisions per second, which speeds the reaction up.

Problem 2

According to collision theory, a collision leads to a reaction only if the particles have…
  1. opposite electric charges
  2. any amount of energy at all
  3. enough energy and the correct orientation
  4. exactly the same mass
Answer and explanation

enough energy and the correct orientation

An effective collision needs at least the activation energy and the proper orientation of the colliding particles.

Problem 3

A reaction produces 90. mL of gas in 45 s. What is the average rate of gas production in mL/s?
Answer and explanation

2 mL/s

Average rate = 90 mL ÷ 45 s = 2.0 mL/s.

Problem 4

Adding more reactant to a system at equilibrium shifts the equilibrium…
  1. so the reaction stops
  2. in no direction
  3. toward whichever side is exothermic
  4. toward the products
  5. toward the reactants
Answer and explanation

toward the products

By Le Châtelier's principle, the system shifts toward the products to consume the extra reactant.

Problem 5

At dynamic equilibrium…
  1. all reaction has stopped
  2. the forward and reverse reactions occur at equal rates
  3. only the forward reaction still occurs
  4. reactant and product amounts must be equal
Answer and explanation

the forward and reverse reactions occur at equal rates

Both reactions continue, but at equal rates, so concentrations stay constant — dynamic, not stopped.

Problem 6

Explain the following claim and supply a valid example or counterexample: Concentration effects depend on the rate law; catalysts do not change equilibrium yield.
Answer and explanation

The kinetic pathway and rate change; overall reaction ΔH and equilibrium K stay the same at fixed conditions. Concentration effects depend on the rate law; catalysts do not change equilibrium yield.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 7

Independent chapter check: A selected rate law is r=k[A]²[B]. Doubling A and halving B at the same temperature changes rate by what factor? If r uses M/s, give k units and one condition needed for the prediction.
Answer and explanation

The factor is 2²×0.5=2. For total order three, k units are M⁻²s⁻¹. Assume the same law, temperature, medium and relevant pathway remain valid; the change does not establish a new mechanism.

The factor is 2²×0.5=2. For total order three, k units are M⁻²s⁻¹. Assume the same law, temperature, medium and relevant pathway remain valid; the change does not establish a new mechanism.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 8

Explain the following claim and supply a valid example or counterexample: Equal forward/reverse rates do not imply equal concentrations or that events stop.
Answer and explanation

Reduced volume raises partial pressures; the adjustment favors the side with fewer gas moles, ammonia, under the model. Equal forward/reverse rates do not imply equal concentrations or that events stop.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 9

Independent chapter check: A⇌B has K=[B]/[A]=4 under a selected ideal concentration convention. Initially at equilibrium [A]=0.20 M and [B]=0.80 M. Add A to 0.70 M at unchanged volume/T. Find immediate Q and predict net direction without claiming original concentrations return.
Answer and explanation

Q=0.80/0.70≈1.14<4, so net forward conversion is favored. Under the closed 1:1 model total concentration becomes 1.50 M and final values are A=0.30 M, B=1.20 M; the ratio returns, not the original amounts.

Q=0.80/0.70≈1.14<4, so net forward conversion is favored. Under the closed 1:1 model total concentration becomes 1.50 M and final values are A=0.30 M, B=1.20 M; the ratio returns, not the original amounts.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 10

For A⇌2B, [A]=.50,[B]=.20 at equilibrium. Find K.
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

0.08

(.20)²/.50=.08.

Problem 11

What changes K: a catalyst or temperature?
Answer and explanation

Temperature can change K; a catalyst alone cannot.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 12

Independent chapter check: For 2A⇌A₂ under the normalized ideal convention, K=2.00, [A]=0.400 M and [A₂]=0.160 M. Compute Q, predict net direction, and state the maximum A₂ concentration if only an initial 0.800 M A inventory were available at fixed volume.
Answer and explanation

Q=0.160/(0.400)²=1.00<2.00, so net forward is favored. From an initial 0.800 M A-only inventory, conservation limits A₂ to at most 0.400 M. The equilibrium value need not reach that maximum, and no rate is given.

Q=0.160/(0.400)²=1.00<2.00, so net forward is favored. From an initial 0.800 M A-only inventory, conservation limits A₂ to at most 0.400 M. The equilibrium value need not reach that maximum, and no rate is given.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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