The Contact process is a classic example of a reversible reaction. Think of it like a seesaw: when one side goes up, the other goes down. The reaction can go forward (producing sulphur trioxide) or backward (reforming sulphur dioxide). The symbol equation is:
\$2\,\mathrm{SO}2(g)+\mathrm{O}2(g)\rightleftharpoons 2\,\mathrm{SO}_3(g)\$
Exam Tip: Remember that the double arrow (⇌) means the reaction can go in both directions. In exam questions, if they ask for the “symbol equation,” include the double arrow and the correct stoichiometric coefficients.
| Condition | Typical Value |
|---|---|
| Temperature | 400–600 °C |
| Pressure | 1–2 atm |
| Catalyst | Vanadium(V) oxide (V₂O?? ) |
Tip: When writing the symbol equation, double‑check the stoichiometric coefficients. A common mistake is to forget the factor of 2 on both sides.
Tip: Use the phrase “the reaction is reversible” to show you understand the double arrow.
Tip: For catalyst questions, remember that a catalyst does not appear in the equation but you can mention it in your answer.
Which of the following is the correct symbol equation for the Contact process?
Answer: 2 – the coefficients must balance on both sides and the double arrow indicates reversibility.
The Contact process converts sulphur dioxide to sulphur trioxide in a reversible reaction. The symbol equation is \$2\,\mathrm{SO}2(g)+\mathrm{O}2(g)\rightleftharpoons 2\,\mathrm{SO}_3(g)\$. Key points for exams include recognising the double arrow, understanding the role of the catalyst, and knowing how temperature and pressure affect the equilibrium. Use the coloured boxes above as quick reminders when you study or during exam preparation. Good luck! 🚀