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Delivery guides are designed to represent a body of knowledge about teaching a particular topic and contain:
- Content: A clear outline of the content covered by the delivery guide;
- Thinking Conceptually: Expert guidance on the key concepts involved, common difficulties students may have, approaches to teaching that can help students understand these concepts and how this topic links conceptually to other areas of the subject;
- Thinking Contextually: A range of suggested teaching activities using a variety of themes so that different activities can be selected which best suit particular classes, learning styles or teaching approaches.
Mathematical learning outcomes:
CM5.2i arithmetic computation, ratio when measuring rates of reaction
CM5.2ii drawing and interpreting appropriate graphs from data to determine rate of reaction
CM5.2iii determining gradients of graphs as a measure of rate of change to determine rate
CM5.2iv proportionality when comparing factors affecting rate of reaction
Assessable content statements:
C5.2a recall that some reactions may be reversed by altering the reaction conditions
C5.2b recall that dynamic equilibrium occurs in a closed system when the rates of forward and reverse reactions are equal
C5.2c predict the effect of changing reaction conditions on equilibrium position and suggest appropriate conditions to produce as much of a particular product as possible (to include Le Chatelier's principle concerning concentration, temperature and pressure)
The reactions studied so far in this course have been one way reactions, so that once the product is formed the reaction finishes. Now learners are introduced to the idea that products sometimes return to reactants. Once the idea of equilibrium- when the concentrations of the products and reactants remain constant - is understood, then they can predict the ideal conditions for important reversible reactions.
The Equilibria Teaching Resources activity uses physical models to aid understanding of equilibria, which once mastered can be applied to chemical equilibria. While the scope for practical work is not as great as in the rest of the topic, there are some simple reversible reactions which can be investigated by learners, for example the ‘magic blue bottle’ described in the Equilibria Teacher Pack, along with some very motivating teacher demonstrations. It is important to stress that these are not the reversible physical reactions that learners have already encountered, such as melting. Using Le Chatelier’s Principle is a useful revision activity, where learners can apply knowledge gained on equilibria to explain observations from an equilibrium reaction.
Common misconceptions or difficulties learners may have
Many learners think that equilibrium is a balanced state of a reaction, failing to appreciate that reversible chemical reactions are always producing products and reactants at the same time, i.e. a dynamic equilibrium. Learners are used to reversible physical processes, but it is important to stress that equilibrium reactions are not physical reactions. They may think that the forward and reverse reactions are equal at equilibrium, rather than the concentrations of the reactants and products remaining constant.
Conceptual links to other areas of the specification – useful ways to approach this topic to set learners up for topics later in the course
This section builds on C3 Chemical Reactions so learners should be familiar with chemical symbols and formulae for elements and compounds. They should also be familiar with representing chemical reactions using formulae, which is vital for understanding the effects of pressure on reversible reactions.
While equilibria is only encountered in this topic, it will be explored further at A-level, by quantifying amounts so that equilibrium constants (Kc) can be calculated. In C6 Global Challenges, the Haber Process will be revisited, in the context of agricultural production.
Approaches to teaching the content
The understanding of dynamic equilibria is fundamental to much of the UK inorganic chemical industry, which is a major contributor to the country’s economy. The Haber Process for the production of ammonia is the classic example. The Ammonia task enables learners to explore the chemistry behind this industry. The Equilibria Pack focuses on reversible reactions which learners can carry out themselves: heating ammonium chloride and hydration of cobalt chloride. Starter for Ten: 8 Equilibria, provides a good range of starters and opportunities for assessment for learning, allowing staff to see if the learners are ready to progress to the next step.
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