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Ideas about equilibria give a solid foundation to students' understanding of the more advanced concepts of acid and base chemistry. There is a whole, separate, course to support teaching about chemical equilibria (future link).

Consider what might students find difficult about equilibria that would apply to this topic?

Students often find it tricky to appreciate that equilibrium is dynamic and not static, as it looks to the naked eye (the macroscopic scale) as though nothing much is happening, but at the sub-microscopic scale at equilibrium, the rate of the forward direction is equal to the rate of the reverse direction.

An equilibrium can be approached from both directions (from reactants or products).

A closed system is necessary for an equlibrium to be set-up. Students sometimes overlook that an open beaker containing a solution is a closed system because the reacting particles cannot escape from the solution and container.

At equilibrium the concentrations of reactants and products are constant. However, students often confuse this and think that the concentrations must be equal, when they are, most often, not equal.

How could models of equilibria help?

Using models of equilibria in class may be very helpful, as many students respond well to hands on activities when they might normally switch off to difficult concepts. Using models can support students in developing their understanding of difficult concepts and to formulate their own explanations clearly.

What sort of models of equilibria are available?

There are many possible active models of equilibria. One simple example for modelling equilibria involves the transfer of water between two containers. pdf EEQUIL5 activity from the F2F course (I'll ask for the pdf of this single activity) Starting with two tanks or plastic tubs, one half full with water, the other empty, a student can use two beakers of different sizes to transfer the water between the containers to model the simultaneous forward and backward reactions. The volume of water transferred represents the rate of reaction. The system has reached equilibrium when the volume of water in the tanks is constant, and most likely not equal.

The Royal Society of Chemistry's Assessment for Learning resources, Equilibrium reactions provides useful tools for clarifying key ideas about equilibria.

A helpful source of information about students' difficulties with equilibria is available in section 12 of  V Kind, Beyond appearances: Students' misconceptions about basic chemical ideas (2nd ed.) Royal Society of Chemistry, 2004.