Kinetics
The first year of A level kinetics largely revises and refines the material that students will be familiar with from GCSE. Collision theory is revisited and consolidated and experimental methods of determining the rate of reaction are expanded upon. Students are expected to be able to state and explain the effect of variables such as reactant concentration, temperature, surface area, pressure and the presence of a catalyst on the rate of a chemical reaction. They should start to move towards a more rigorous definition of rate in terms of the rate of change of concentration with time (units of mol dm-3s-1).
However there is little new material in this first part of the A level course apart from the introduction of the Boltmann distribution. Students learn the importance and form of the Boltmann distribution and must be able to use graphs to explain the effect of temperature and catalysis on the rate of reaction.
Apart from calculation of rate from the gradient of curves on time, the treatment of kinetics in year one is qualitative.
It is in the second year that a more rigorous approach is taken to the study of reaction kinetics and the treatment becomes quantitative. Students need to understand experimental approaches to determination of rate with a greater level of detail, including the difference between a continuous monitoring method and one employing an initial rate approach. In addition the concept of the chemical rate equation is introduced along with order of reaction and partial orders, and students must become adept at deducing the partial order of reaction of a species from given numerical or graphical data.
The importance of kinetics in determining reaction mechanisms is explored, and students need to learn to be able to identify the rate limiting step in a reaction given the form of the chemical and rate equation. This is an area that students need practice in to become proficient. Some syllabuses apply this understanding to deducing whether a given substrate will react via an SN1 or an SN2 mechanism in nucleophillic substitution. This discussion is instructive whether on syllabus or not, as it provides a simple exemplar that students will be familiar with to a greater or lesser degree. (ALL syllabuses include the SN2 mechanism whether explicitly named or not).
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Reaction Rates and Mechanisms *suitable for home teaching*
This activity gives students experimental data and asks them to work out the order of reaction and reaction mechanism from it. The resource also contains teacher notes.
Unit P5: Chemical Kinetics *suitable for home teaching*
A comprehensive resource that covers most of the kinetics content at A level. The topics covered are rates of reaction and rate equations, reaction mechanisms, activation energy, catalysis and collision theory. Each chapter contains a set of questions and relevant practical investigations. Although the formating is quite dated, it is a very handy resource to have on hand.