How is carbon dioxide formed? Write two equations and give three uses of carbon dioxide.

1. 1 · Formation by burning. Carbon burns in plenty of oxygen: C + O₂ → CO₂. Fuels too: CH₄ + 2O₂ → CO₂ + 2H₂O.
2. 2 · Other ways. Heating carbonates: CaCO₃ → CaO + CO₂. Fermentation of glucose also gives CO₂.
3. 3 · Uses.
   • Dry ice, a refrigerant (sublimes at −78 °C)
   • The fizz in carbonated drinks
   • Making washing soda and baking soda
4. 4 · Real life. It is a main cause of the greenhouse effect, so burning less fuel helps.
5. 5 · Close in one line. So carbon dioxide forms whenever carbon compounds burn completely.

Scoring tip: Balance the methane equation: one CH₄ needs two O₂ and gives two H₂O.