Another way of illustrating a dynamic equilibrium is by using 'princess and toad' cards.

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Activity directions

Twenty-four cards are produced with a picture of a princess on one side and a picture of a toad on the other side. Students assume the role of a 'good' witch or wizard and a 'bad' witch or wizard. One student (bad wizard) turns over the princess pictures to reveal toads while the other student (good wizard) turns over pictures of toads to reveal princesses. The students are illustrating the forward or reverse reaction in a reversible reaction.

Scenario 1

The cards are all placed with the toad uppermost. One student turns over all the cards to reveal princesses. Another student turns all the cards to reveal the toads again.
 

What do these two steps represent in the context of a chemical reaction?

They represent a reaction that can be reversed.

Scenario 2

Next, the cards are set out with all toads showing. One student turns over the cards one by one to reveal princesses. When 12 cards have been turned over another student starts to turn the cards showing princesses over to reveal toads. After about 4 minutes the students stop and count the number of cards showing toads and princesses.

What does this process represent in terms of a chemical reaction?

A reaction in which an equilibrium is established.

What would you expect the number of toads to be after 4 minutes?

The number of toads will be about 12. 

Like all analogies, care must be taken to identify its strengths and weaknesses in relation to the concept it is used to illustrate, and to prevent the analogy reinforcing student misconceptions.

What student misconceptions might this analogy inadvertently reinforce?

The idea that the forward and reverse processes are separate reactions.
The idea that forward and reverse reactions are sequential rather than simultaneous changes.
The idea that the amount of reactants and products is the same.