The Contact Process (Chemistry)

Lesson notes

Overview

Sulfuric acid, the most produced industrial chemical, is made by oxidising SO₂. This topic is rated advanced and is number 103 of 110 in Chemistry. Deeper models, formal results and harder reasoning.

What you are seeing

The panel above shows the steps of a process, laid out in order. Click a step to see what happens next. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.

In depth

The contact process makes sulfuric acid, the world’s most-produced industrial chemical, used for fertilisers, detergents and batteries. Sulfur is burned to SO₂, which is oxidised to SO₃ over a vanadium(V) oxide catalyst at about 450 °C and 1–2 atm, 2SO₂ + O₂ ⇌ 2SO₃. The SO₃ is absorbed into concentrated sulfuric acid to make oleum and then diluted, since adding it directly to water would produce a dangerous mist.

Reading the relationship

The expression "2SO₂ + O₂ ⇌ 2SO₃" is a compact summary of the idea. It uses the symbols S, O₂, O₃; name what each one stands for before you start. Then use the sliders to see how changing one quantity changes the others.

A guided exploration

1. Run the animation once with the default settings and describe in words what happens. 2. Change one slider at a time and note which quantity responds most. 3. Push each slider to its extreme and decide whether the result still makes sense.

Try this

Try to explain why the pattern holds, not just what it is. Look for limiting cases and what happens at the edges.

Common pitfalls

Keep the particle picture in mind. Mistakes often come from treating a rate, an amount and an equilibrium position as the same thing, or from ignoring units and conditions.

How it connects

It builds on “Making Ammonia to Feed the World”, the topic before it in Chemistry. Once you are comfortable, continue with “Water Treatment”.

Why it matters

Chemistry links the tiny scale of atoms to the materials, medicines and energy we use every day.

Where you might use it

Revising “The Contact Process” before a class, exam or certification
Predicting how fast a reaction runs in a lab or an industrial plant
Choosing materials, medicines and fuels based on how their atoms bond and react
Reading the labels and data sheets of cleaning products, batteries and food

Frequently asked questions

What is The Contact Process?

Sulfuric acid, the most produced industrial chemical, is made by oxidising SO₂. It is an advanced topic in Chemistry.

How do I use the The Contact Process simulation?

The panel at the top shows the steps of a process, laid out in order. Click a step to see what happens next. Move the sliders one at a time, then press Space to pause the animation and look closer.

What does the formula mean?

The expression 2SO₂ + O₂ ⇌ 2SO₃ packs the idea into symbols. Name each symbol first, then change one quantity with the sliders and see which others respond.

Who is this topic for?

Deeper models, formal results and harder reasoning. If the quiz feels hard, reread the lesson notes and try the previous topic first.

What should I learn before this?

Start with “Making Ammonia to Feed the World”, the previous topic in Chemistry. Each topic in a subject builds on the ones before it.

How do I track my progress?

Press “Mark as learned” on this page. Progress is stored only in this browser and is never sent anywhere. The Browse page can show topics you have learned or still need to learn.