6. Chemical kinetics

6. Chemical kinetics

6.1 Collision theory and rates of reaction

Nature of science:

  • The principle of Occam’s razor is used as a guide to developing a theory - although we cannot directly see reactions taking place at the molecular level, we can theorize based on the current atomic models. Collision theory is a good example of this principle.

Understandings:

  • Species react as a result of collisions of sufficient energy and proper orientation.

  • The rate of reaction is expressed as the change in concentration of a particular reactant/product per unit time.

  • Concentration changes in a reaction can be followed indirectly by monitoring changes in mass, volume and colour.

  • Activation energy (Ea ) is the minimum energy that colliding molecules need in order to have successful collisions leading to a reaction.

  • By decreasing Ea , a catalyst increases the rate of a chemical reaction, without itself being permanently chemically changed.

Applications and skills:

  • Description of the kinetic theory in terms of the movement of particles whose average kinetic energy is proportional to temperature in Kelvin.

  • Analysis of graphical and numerical data from rate experiments.

  • Explanation of the effects of temperature, pressure/concentration and particle size on rate of reaction.

  • Construction of Maxwell–Boltzmann energy distribution curves to account for the probability of successful collisions and factors affecting these, including the effect of a catalyst.

  • Investigation of rates of reaction experimentally and evaluation of the results.

  • Sketching and explanation of energy profiles with and without catalysts.

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