International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

Which of the following equations represents a combustion reaction in a blast furnace?

1. C + O₂ -> CO₂

2. SiO₂ + CaO -> CaSiO₃

3. CaCO₃ -> CaO + CO₂

4. C + CO₂ -> 2CO

The correct answer is: C + O₂ -> CO₂

A combustion reaction is characterized by the reaction of a fuel with oxygen, resulting in the release of energy and often the production of carbon dioxide and water. In the context of a blast furnace, carbon (often in the form of coke) is used as a fuel to produce heat necessary for the reduction of metal ores. The equation representing the combustion of carbon involves carbon reacting with oxygen to produce carbon dioxide. This is a classic example of a combustion reaction, as it involves the combination of carbon and oxygen. The process generates heat, which is essential for the operation of the blast furnace where iron ore (usually iron(III) oxide) is reduced to produce iron. Other options provided relate to different types of chemical reactions that do not fit the criteria for a combustion reaction. The reaction of silicon dioxide and calcium oxide represents a formation of a compound (slag) utilized in metallurgy but does not involve combustion. The thermal decomposition of calcium carbonate to produce calcium oxide and carbon dioxide is also not a combustion reaction. The fourth option describes the reduction of carbon dioxide by carbon, producing carbon monoxide, which is a reduction process rather than a combustion one. Thus, the equation C + O₂ -> CO₂ correctly depicts the combustion process that occurs in a blast furnace