Rate of Reaction
The resources in this list cover rates of reaction, how they can be measured, and what factors affect the rate of a chemical reaction.
Students need to understand how the rate of a chemical reaction can be measured in terms of the rate of production of a product or the rate of consumption of a reactant. Students also need to be able to describe simple methods of measuring mass loss if a gaseous product is allowed to escape, volume of gas produced , change in colour, change in pH, or change in turbidity if a precipitate is produced.
Students should be able to produce graphs of amount of species (as mass, volume or some relative quantity) against time and understand that the gradient to the curve at any point in time represents the rate of reaction at that time.
Higher tier students need to be able to use concentration as the measure of amount of species and calculate the numerical value of the gradient at a point on the curve.
Students need to be able to identify factors that affect the rate of a chemical reaction and to predict and explain the effect of changing a factor using collision theory.
Students should represent reactions and reaction profiles and clearly identify the activation energy and enthalpy change, and be able to sketch a suggested profile for a catalysed reaction on the uncatalysed profile to show the difference.
Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS, SSERC or other recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance
Links and Resources
Although catalysts are not changed chemically by a reaction the do take part in the reaction. Very often they are chemically changed in one step of a reaction but regenerated in another. This demonstration from the RSC enables students to see the evidence for this in terms of a colour change as the reaction progresses. The reaction is between hydrogen peroxide and potassium sodium tartarate to produce hydrogen peroxide. The reaction is catalysed by Co2+ ions, which give a pink colour to the reaction mixture. The pink becomes green as catalysis takes place, due to formation of an activated complex containing cobalt ions and then goes back to pink as the Co2+ ions are regenerated. At this level it can be simply stated that the cobalt ions turn green when they catalyse the reaction without explaining why in terms of activated complexes and transition states which are undergraduate level topics.
This resource describes the use of a potassium iodate and starch reaction to investigate the effect of concentration and temperature (independently) on rate of reaction. The protocol is quite detailed in how to make up the reagents and run the reaction but is more sketchy on its use in an investigation and teachers need to be comfortable deciding on a suitable range of temperatures and concentrations to work with. The method mentions the use of ICT to monitor the production of coulour but this is not strictly necessary and students can watch for the appearance of colour instead if so wished. The sheet includes an explanation of how the reaction works which may be useful to teachers as background but is A level standard and is not necessary in order for students to simply use this reaction as an investigative technique when looking at the effect of concentration and temperature on rate.
This resource from the RSC outlines the investigation of the effect of temperature on the rate of reaction using the classical reaction between sodium thiosulphate and hydrochloric acid. As the reaction progresses a precipitate of sulphur is produced and the amount is monitored by looking down through the reaction at a cross on a piece of paper below the flask. The reaction is timed to the point when the cross disappears. For each reaction it is assumed that the same amount of sulphur will have been produced when the cross first disappears and so the time taken is inversely proportional to the rate of the reaction. The resource includes brief teacher notes and a student worksheet.
This resource from the RSC outlines the investigation of the effect of concentration on the rate of reaction using the classical reaction between sodium thiosulphate and hydrochloric acid. As the reaction progresses a precipitate of sulphur is produced and the amount is monitored by looking down through the reaction at a cross on a piece of paper below the flask. The reaction is timed to the point when the cross disappears. For each reaction it is assumed that the same amount of sulphur will have been produced when the cross first disappears and so the time taken is inversely proportional to the rate of the reaction. The resource includes brief teacher notes and a student worksheet.
The first section of this resource is on collision theory and gets students to consider the effect of changing the conditions of a reaction (concentration, volume, particle size or temperature) on the graph that would be expected under those conditions. This is a common exam type question and students need to think about both the total amount (in this case volume) of product produced and also the rate at which it is produced. Students need to have covered mole calculations, particularly of solutions, in order to gain benefit from this activity.