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.