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In this unit students learn about the factors affecting rates of reaction and how to express rates quantitatively. Material covered includes Rates of reaction, collision theory, rate expression, reaction mechanism and activation energy.

Essential idea

The greater the probability that molecules will collide with sufficient energy and proper orientation, the higher the rate of reaction.

Learning Targets


Life-Long Learners - Careful observation and recognition of patterns of behavior allows us to make predictions about the behavior of the natural world.

Topic 6: Kinetics (5 hours)

6.1 Rates of reaction

  • Define the term rate of reaction
  • Describe suitable experimental procedures for measuring rates of reactions
  • Analyse data from rate experiments

6.2 Collision theory

  • Describe the kinetic theory in terms of the movement of particles whose average energy is proportional to temperature in kelvins
  • Define the term activation energy, Ea
  • escribe the collision theory
  • Predict and explain, using the collision theory, the qualitative effects of particle size, temperature, concentration and pressure on the rate of a reaction
  • Sketch and explain qualitatively the Maxwell–Boltzmann energy distribution curve for a fixed amount of gas at different temperatures and its consequences for changes in reaction rate
  • Describe the effect of a catalyst on a chemical reaction
  • Sketch and explain Maxwell–Boltzmann curves for reactions with and without catalysts

Topic 16: Kinetics (HL students only)

16.1 Rate expression

  • Distinguish between the terms rate constant, overall order of reaction and order of reaction with respect to a particular reactant
  • Deduce the rate expression for a reaction from experimental data
  • Solve problems involving the rate expression
  • Sketch, identify and analyse graphical representations for zero-, first- and second-order reactions

16.2 Reaction mechanism

  • Explain that reactions can occur by more than one step and that the slowest step determines the rate of reaction (rate-determining step)
  • Describe the relationship between reaction mechanism, order of reaction and rate-determining step

16.3 Activation energy

  • Describe qualitatively the relationship between the rate constant (k) and temperature (T)
  • Determine activation energy (Ea) values from the Arrhenius equation by a graphical method

The detailed curriculum can be consulted here.

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