Effects of Greenhouse Gases
Section: 10. Chemistry of the Environment | Syllabus: Cambridge IGCSE Chemistry (0620)
How Greenhouse Gases Cause Global Warming (Supplement)
The greenhouse gases carbon dioxide and methane cause global warming through the absorption, reflection and emission of thermal energy:
- Thermal energy is emitted from the Earth's surface (as it re-radiates the energy it absorbed from the Sun).
- Greenhouse gases in the atmosphere absorb this thermal energy.
- Greenhouse gases then emit thermal energy back towards the Earth.
- The result is reduced thermal energy loss to space - energy that would otherwise escape is instead sent back down, so the Earth warms up.
Worked Example
- Question (based on a real exam diagram): a diagram shows "emission of thermal energy from the Earth" → X → Y → Z, with a feedback arrow from Z back to X. Identify X, Y and Z.
- Answer: X = absorption of thermal energy by greenhouse gases; Y = emission of thermal energy to the Earth; Z = reduced thermal energy loss to space.
Common Mistakes
- ❌ Thinking greenhouse gases cause warming by emitting thermal energy into space, or that the result is increased energy loss to space
- ✓ it's the opposite - greenhouse gases absorb outgoing thermal energy and emit it back towards the Earth, so less energy escapes to space; that trapped energy is what causes warming
Formation and Removal of Oxides of Nitrogen (Supplement)
Oxides of nitrogen form inside car engines, where the high temperatures of combustion allow nitrogen and oxygen from the air to react directly with each other:
nitrogen + oxygen → nitrogen dioxide
Catalytic converters fitted to vehicle exhausts remove oxides of nitrogen by reacting them with carbon monoxide (itself a pollutant from incomplete combustion), converting both into harmless products:
2CO + 2NO → 2CO₂ + N₂
Worked Example
- Question: (i) write a word equation to show how nitrogen dioxide is produced from two gases present in air. (ii) State two adverse effects of nitrogen dioxide in air.
- Answer: (i) nitrogen + oxygen → nitrogen dioxide; (ii) any two of - acid rain; photochemical smog; respiratory problems.
Interactive revision notes, videos and practice questions load below.