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

Which of the following correctly describes the products of the balanced equation WO₃ + 3H₂ -> W + 3H₂O?

1. One tungsten atom and three water molecules

2. Three tungsten atoms and one water molecule

3. Three water molecules and one tungsten atom

4. One tungsten atom and three hydrogen molecules

The correct answer is: One tungsten atom and three water molecules

The balanced equation WO₃ + 3H₂ -> W + 3H₂O shows that one mole of tungsten trioxide (WO₃) reacts with three moles of hydrogen gas (H₂) to produce one mole of tungsten (W) and three moles of water (H₂O). By analyzing the products of the reaction, one can clearly identify that the products consist of one atom of tungsten and three molecules of water. The equation indicates that tungsten is generated from the reduction of tungsten trioxide, and for every mole of WO₃ consumed, one mole of W is produced. Simultaneously, the three water molecules produced correspond to the three moles of H₂ used in the reaction. This underscores that option A accurately states the quantities of the products formed in the reaction, capturing the essential stoichiometry in the balanced equation.