Question: Calculate the mass of CO₂ produced when 1 kg of octane (C₈H₁₈) burns completely.
Solution:
- Balanced equation: 2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O
- Molar masses: Mr(C₈H₁₈) = (8 × 12) + (18 × 1) = 114 g/mol; Mr(CO₂) = 12 + (2 × 16) = 44 g/mol
- Mole ratio: 2 mol C₈H₁₈ → 16 mol CO₂; so 1 mol C₈H₁₈ → 8 mol CO₂
- Mass ratio: 114 g C₈H₁₈ → 8 × 44 = 352 g CO₂
- For 1 kg (1000 g): CO₂ = (1000 ÷ 114) × 352 = 3090 g = 3.09 kg
Answer: 1 kg of octane produces about 3.09 kg of CO₂ — showing why transport is such a large contributor to emissions.
This worked example covers Worked Example: CO₂ from Fuel Combustion within Climate Change for GCSE Chemistry. Revise Climate Change in Atmosphere for GCSE Chemistry with 20 exam-style questions and 15 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 10 of 17 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Practice questions for Climate Change
Which statement correctly describes the difference between weather and climate?
Explain three consequences of climate change for the environment or human populations. [3 marks]