Flow diagrams are a very effective way of presenting a large amount of complex information in a clear and visual format. The example below is based on the production of sulfuric acid by the Contact process. Asking students to label the diagram helps check that they can understand what the diagram means.

Molten sulfur is burnt in air to form sulfur dioxide:

S(l) + O₂(g) _↓ SO₂(g)

The sulfur dioxide is heated in a heat exchanger and passed with air into a reaction vessel containing a vanadium(V) catalyst where it is converted into sulfur trioxide:

2SO₂(g) + O₂(g) _∏ 2SO₃(g)

The sulfur trioxide is dissolved in concentrated sulfuric acid and this mixture is diluted to produce 98% sulfuric acid.

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Use the flow diagram to identify the materials A to F in the following drag and drop activity.

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When students have become familiar with the conventions that are used in flow diagrams they can be asked to devise their own examples. This is a much higher level skill because it requires them to reduce the complex information into a limited number of related steps.