The Contact Process and Sulfuric Acid
Sulfur dioxide is oxidised to make the world's most-made acid.
About this topic
The contact process makes sulfuric acid, the most widely produced industrial chemical. Sulfur is burned to give sulfur dioxide (S + O2 → SO2), which is oxidised to sulfur trioxide using a vanadium(V) oxide catalyst: 2SO2 + O2 ⇌ 2SO3. The trioxide is absorbed in concentrated sulfuric acid to form oleum, which is diluted with water to give H2SO4.
Conditions are about 450 degrees Celsius and 1 to 2 atmospheres. The conversion step is exothermic and has fewer gas moles on the right, so low temperature and high pressure favour SO3, but again the rate is too slow at low temperature, and since yield is already about 99 percent at near atmospheric pressure, extra pressure is unnecessary. Dissolving SO3 directly in water would give a dangerous acid mist, so it is absorbed in 98 percent sulfuric acid first. The reaction is highly exothermic, and the heat is used to generate steam.
Sulfuric acid is used for fertilisers (superphosphate and ammonium sulfate), detergents, paints, car batteries, metal cleaning and many chemical syntheses; a country's consumption has long been seen as a measure of its industrial strength. Concentrated acid is a powerful dehydrating agent, turning sugar into black carbon.
A misconception is that SO3 is dissolved straight in water; it is not. Also, never add water to concentrated sulfuric acid, because the heat can make it spit.
Key ideas
- Vanadium oxide catalyst
- Used in fertilisers and batteries
- SO₂ → SO₃ → H₂SO₄
Quick check
Use cases: where The Contact Process and Sulfuric Acid helps
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Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is The Contact Process and Sulfuric Acid?
Sulfur dioxide is oxidised to make the world's most-made acid.
What will I learn in The Contact Process and Sulfuric Acid?
Vanadium oxide catalyst. Used in fertilisers and batteries. SO₂ → SO₃ → H₂SO₄.
Is The Contact Process and Sulfuric Acid part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the The Contact Process and Sulfuric Acid lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study The Contact Process and Sulfuric Acid?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
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