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 moldm-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 course, 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 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).
This resource list includes material covering both years of the course, with first year material appearing at the beginning of the list.
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Links and Resources
This comprehensive resource provides much detailed background material on the topics covered in this module. The resource would be useful for teachers when planning lessons, but also many of the exercises, with a few dated exceptions, are still useful and pertinent to current syllabuses and can be scanned or retyped and edited to provide class or homework material. An invaluable resource for planning, and for setting example problems to support teaching and learning.
Here are teacher notes and a student activity sheet covering the classic kinetics investigation of the effect of a reactant concentration on the rate of reaction between sodium thiosulphate and hydrochloric acid.
At A level, the experiment can be usefully extended by discussing the difference between instantaneous rate and the average rate as determined by this experiment. This can then lead to a discussion of the two approaches to rate determination of continuous monitoring and initial rate methods.
An alternative microscale method can be found here.
This is similar to the previous resource, but this time investigates the relationship between temperature and rate.
As it is presented, this experiment provides a rather simple and semi-quantitative approach to investigating the effect of reactant concentration and temperature on the rate of a chemical reaction. Insufficient data is obtained to plot graphs and deduce quantitative relationships.
However, the approach could very easily be extended, increasing the data range, by investigating a range of concentrations and temperatures. The resource would then provide an alternative to experiments with sodium thiosulphate and hydrochloric acid which students may have already met at GCSE.
This resource describes an interesting, and highly visual, qualitative demonstration of the effect of a catalyst on the rate of a chemical reaction involving colour changes as the reaction progresses. The demonstration could usefully be employed during a review of factors affecting the rate of reaction and/or as a preliminary to a discussion of collision theory.
Superficially, this resource seems to be very similar to the pervious one on the effect of a catalyst on a chemical reaction. However, in this case the obseved colour change is due to the interaction of the catalyst in the activated complex.
The demonstration can be nicely linked to the previous one to lead to a discussion of how the catalyst actually works, Students will be aware of the idea of a catalyst providing an alternative pathway of lower energy for the reaction from GCSE, but most will not have discussed transition state theory, and this demonstration can be used to introduce and stimulate ideas on this aspect of catalysis.
This resource provides useful worksheets covering collision theory and the Boltzmann distribution. The material can be used to reinforce learning either in class or as homework exercises.
Another comprehensive resource from the ILPAC collection which provides much detailed background material on the Maxwell-Boltzmann distribution, including details on how the data is obtained (the Zartman experiment).
The resource would be useful for teachers when planning lessons for this topic, but also many of the exercises, with a few dated exceptions, are still useful and pertinent to current syllabuses and can be scanned or retyped and edited to provide class or homework material. An invaluable resource for planning, and for setting example problems to support teaching and learning.
This is a nice little resource which covers the various skills involved in establishing the form of a chemical rate equation from given data, such as deducing partial orders of reaction, and working out the value and units of the rate constant. The resource then continues by linking the form of the chemical rate equation to compatible reaction mechanisms.
It could be usefull set as a class exercise or a homework once these skills have been taught.
This resource gives students an opportunity to apply their understanding of the concepts developed in this module to deducing the mechanism of reaction between iodine and propanone. It is designed to be carried out in groups, and to fit into a time span of two hours.
Some preparatory work is needed and students sheets are provided for this. Teacher notes including answers to the preparatory questions and a suggested solution to the problem are included.