C5.1 Controlling reactions
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C5.1 Controlling reactions
Mathematical learning outcomes:
CM5.1i arithmetic computation, ratio when measuring rates of reaction
CM5.1ii drawing and interpreting appropriate graphs from data to determine rate of reaction
CM5.1iii determining gradients of graphs as a measure of rate of change to determine rate
CM5.1iv proportionality when comparing factors affecting rate of reaction
Assessable content statements:
C5.1a suggest practical methods for determining the rate of a given reaction
C5.1b interpret rate of reaction graphs (to include 1/t is proportional to rate and gradients of graphs)
C5.1c describe the effect of changes in temperature, concentration, pressure, and surface area on rate of reaction
C5.1d explain the effects on rates of reaction of changes in temperature, concentration and pressure in terms of frequency and energy of collision between particles
C5.1e explain the effects on rates of reaction of changes in the size of the pieces of a reacting solid in terms of surface area to volume ratio
C5.1f describe the characteristics of catalysts and their effect on rates of reaction
C5.1g identify catalysts in reactions
C5.1h explain catalytic action in terms of activation energy (to include reaction profiles)
C5.1i recall that enzymes act as catalysts in biological systems
Chemical reactions, such as those happening in our bodies, in the world around us and in the chemical industry can be affected by changes such as temperature, pressure, size and concentration of reactants, so the factors that affect their rate are studied in detail in this sub-topic. This part of the delivery guide provides scope for developing the necessary practical, mathematical and thinking skills involved in studying and controlling common reactions.
There are many suitable and motivating practicals which can be studied to illustrate the theory used to explain results, such as Marble Chips and Acid, Disappearing Cross Experiment and Rates and Rhubarb. The Collision Theory activity encourages deep understanding of the theory which underpins this subtopic via a number of activities on catalysts and activation energy, rates of reaction graphs, as well as the collision theory.
Common misconceptions or difficulties learners may have
Learners may think that chemical reactions are instantaneous, as many which are used in school appear to be so, to maintain learner engagement. The rusting of iron is a useful illustration of a slow reaction. Learners may misinterpret rate graphs, so it is important that data collected is plotted and analysed in plenary sessions. As catalysts are added to reaction mixtures and rarely removed, it is possible for learners to think that they are used up. It may benefit such learners to explain that the catalyst is changed during the reaction (by forming an intermediate compound) but always returns to its original chemical form by the end of the reaction.
Conceptual links to other areas of the specification – useful ways to approach this topic to set learners up for topics later in the course
The collision theory builds on the particle theory which was developed in C1 and can be used to explain reactions. Rates are revisited in C6 Global Challenges in the context of the Haber Process and Contact Process to produce a cost-effective product. At A Level, the study of rates is quantified by calculating rate constants.
A class experiment for investigating the effect of temperature on the rate of the reaction (PAG C1, 8).
This reaction is also suitable for investigating the effect of concentration on the rate of reaction.
Approaches to teaching the content
Continuing with the experimental nature of the topic as a whole, this section provides a wide range of practical activities which can be used for PAG C1, so it is crucial that learners are provided with practical opportunities to develop appropriate practical skills. They should also become used to plotting data and analysing it mathematically, for example, by calculating gradients at different points in the reaction to show how the rate changes during the reaction.
Starter for Ten provides a starter activity for a quick check on prior learning for a revision lesson. It can be useful to provide mini-whiteboards so that all the class are involved. This could be followed up with the Rates of Reaction Graphs activity. Who Sank the Kursk? puts the use of catalysts in the context of finding out what sank the Russian nuclear submarine Kursk, which can be very motivating, showing the relevance of studying rates of reactions. It begins with stimulus material in the form of a text document and a teacher demonstration. After checking and evaluating their experimental plan learners carry out practical work, share results and agree on conclusions. Finally, they work in groups to extract information from unfamiliar but contemporary texts. Testing for Enzymes provides an engaging experiment to show that enzymes are found in common foods and this could be followed up with research on other uses of enzymes in the food industry. Such activities should provide plenty of opportunities for assessment for learning.
Learners plan an investigation into the effect of catalysts on the rate of a reaction.
The activity is placed in the context of finding out what sank the Russian nuclear submarine Kursk (PAG C1,8) .
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