Student misconceptions about equilibria are discussed in detail by Vanessa Kind on page 70 of Beyond appearances: Students' misconceptions about basic chemical ideas.

Research shows that some students associate a chemical equilibrium with:

• the idea of balancing;
• a see-saw;
• a static process with reactants and products in equal amounts.

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What is the problem associated with the first three meanings?

The first three meanings imply wrongly that no change occurs when an equilibrium is established. This is why it's important to stress that at equilibrium changes are still going on.

Why might students think that at equilibrium the amounts of reactants and products are equal?

The idea that the amounts of reactants and products at equilibrium are equal probably comes from the 'balance' idea. It is a confusion with the idea of forces being in balance in physics. In chemical reactions either the forward or reverse reaction may dominate, so amounts or concentrations of reactants and products are rarely equal. This misconception is also suggested by the idea of a see-saw in a horizontal position.

Look at the conversation between two students below.

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What student misconceptions can you identify from the conversation?

Student A thinks that everything stops when equilibrium is reached when in fact particles react continuously. Student B thinks that the forward reactions are separate and occur in turn. This is wrong because the reactions are parts of one reversible reaction. The reverse reaction starts as soon as there are some products in the mixture. Student B also thinks that the amounts of reactants and products are equal at equilibrium, when it is the rates of the forward and reverse reactions that are reversible.