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

Which chemical equation represents the manufacture of ethanol by passing ethene and steam?

1. C₂H₄ + H₂O -> C₂H₅OH

2. C₂H₅OH + CO₂ -> C₆H₁₂O₆

3. H₂ + O₂ -> H₂O

4. C₆H₁₂O₆ -> 2C₂H₅OH + 2CO₂

The correct answer is: C₂H₄ + H₂O -> C₂H₅OH

The manufacture of ethanol by passing ethene and steam is represented by the chemical equation C₂H₄ + H₂O -> C₂H₅OH. In this process, ethene (C₂H₄) reacts with water (H₂O) in the presence of a catalyst, typically phosphoric acid, to produce ethanol (C₂H₅OH). This reaction involves the addition of water to ethene, which is an alkene, in a hydration reaction. The formation of ethanol is significant because it is a valuable industrial chemical used as a fuel, solvent, and in the production of various chemicals. Understanding this reaction highlights the importance of alkenes and their reactivity with water under specific conditions to form alcohols. The other options provided do not represent the described process. One option suggests a reaction involving ethanol and carbon dioxide, which is more aligned with fermentation rather than ethene hydration. Another option depicts the formation of water from hydrogen and oxygen, which is unrelated to ethanol production. Lastly, the equation involving glucose decomposition illustrates fermentation, which is a different method of ethanol production, typically involving biological processes rather than the direct synthesis from ethene and steam.