Reaction Rates & Kinetics — Practice · Grade 11 Science
Chapter: Rates & EquilibriumWhat this practice covers
By the end of Reaction Rates & Kinetics you should be able to:
- I can use collision theory to explain what must happen for particles to react.
- I can predict how concentration, temperature, surface area, and catalysts change the rate of a reaction.
- I can calculate an average reaction rate from the change in an amount over time.
9 questions, multiple choice, numeric and written answer, each with a worked explanation.
Vocabulary used: reaction rate, collision theory, effective collision, catalyst, surface area, inhibitor.
Problem 1
- removing the catalyst
- cooling the reactants
- using large chunks instead of a fine powder
- increasing the concentration of a reactant
Answer and explanation
increasing the concentration of a reactant
Increasing that reactant’s concentration can increase rate under the stated conditions. Concentration effects depend on the actual reaction and rate law; this is not a universal rule for every reaction.
Problem 2
- enough energy and the correct orientation
- that a catalyst be present
- that the reaction be exothermic
- only that the particles touch
Answer and explanation
enough energy and the correct orientation
A collision only produces a reaction if the particles collide with at least the activation energy and are properly oriented.
Problem 3
Answer and explanation
4 mL/s
Rate = 48 mL ÷ 12 s = 4.0 mL/s.
Problem 4
Answer and explanation
Powder has far more exposed surface area than a single lump, so many more zinc atoms are in contact with the acid at once. That allows far more effective collisions per second between zinc and acid particles, which speeds up the reaction.
Problem 5
Answer and explanation
0.008 mol/s
Rate = 0.36 mol ÷ 45 s = 0.008 mol/s.
Problem 6
Hints
Reaction coefficients do not generally supply rate-law exponents.
Answer and explanation
First order, since 2^n=2 gives n=1.
Problem 7
Hints
State what the supplied observations or conditions establish, and separate that from any assumption.
Answer and explanation
It accelerates forward and reverse processes without changing the equilibrium constant at fixed temperature.
Problem 8
Answer and explanation
No. These are normalized distributions. The population is spread over a wider energy range; compare areas and the threshold tail rather than peak height alone.
At thermal equilibrium a gas has a distribution of translational energies, not one common energy per molecule. Raising temperature shifts and broadens the ideal distribution so a greater fraction can exceed a selected activation threshold. This helps explain many temperature effects on rates, though orientation, mechanism and transport also matter. A catalyst changes the pathway/barrier rather than simply raising every molecule’s energy or changing equilibrium. The shaded-free curves here encode a probability density; an area, not peak height alone, represents a fraction.
No. These are normalized distributions. The population is spread over a wider energy range; compare areas and the threshold tail rather than peak height alone.
Response criteria
- Interpret labels, structures, axes, units and directions correctly.
- Explain the chemistry relationship or mechanism.
- Respect stated assumptions and distinguish observation from inference.
Problem 9
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.