The use of both an equals sign and an arrow in equations can be quite confusing to some students. The problem may be that they're unaware they aren't comparing like with like.

The equals sign really represents the situation at the start and at the end of a reaction. In this kind of comparison the mass of reactants and products must be equal, in agreement with the Law of Conservation of Mass.

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How might Lego bricks be used to illustrate the Law of Conservation of Mass?

Lego bricks could be made into models representing reactants. These models can be taken apart and rearranged in a different way to make new models. No bricks are added and none are left over at the end.

The use of an arrow, however, describes a change over time in which reactants are gradually converted into products. It's a description of a journey rather than a comparison of a starting point with the destination. When moving from one way to reversible reactions it becomes essential that an arrow is used so that the direction of change is unambiguous.

How might you raise awareness of the change from reactants to products over time?

You could ask students what is present in the reaction mixture part way through the reaction. It's interesting that we talk about a reaction mixture but never talk about a product mixture. Again Lego bricks can be used to show that the proportion of reactants and products changes over time.