ChemistryCode 5070
Air quality and climate
What this topic asks you to be able to do
- Give the makeup of uncontaminated, moisture-free air: about 78% nitrogen, N2, 21% oxygen, O2, with what remains being a blend of noble gases and carbon dioxide, CO2
- State where each of these air pollutants comes from: (a) carbon dioxide, released when carbon-containing fuels undergo complete combustion (b) carbon monoxide and particulates, released when carbon-containing fuels undergo incomplete combustion (c) methane, released as vegetation undergoes decomposition and in waste gases from animals' digestion (d) oxides of nitrogen, released by car engines (e) sulfur dioxide, released by the combustion of fossil fuels that contain sulfur compounds
- State how these air pollutants cause harm: (a) carbon dioxide: climate change, because higher levels of the gas increase global warming (b) carbon monoxide: it is a toxic gas (c) particulates: a greater risk of cancer and respiratory problems (d) methane: climate change, because higher levels of the gas increase global warming (e) oxides of nitrogen: they cause acid rain, respiratory problems and photochemical smog (f) sulfur dioxide: it causes acid rain
- Describe the mechanism by which carbon dioxide and methane, acting as greenhouse gases, produce global warming, limited to: (a) absorbing, reflecting and emitting thermal energy (b) lowering the rate at which thermal energy is lost to space
- State and explain ways of lessening the harm done by these environmental problems, limited to: (a) climate change: farming fewer livestock, planting trees, using less fossil fuel, and making more use of hydrogen and of renewable energy, e.g. solar, wind (b) acid rain: fitting catalytic converters to vehicles, and cutting sulfur dioxide emissions by switching to low-sulfur fuels and by flue gas desulfurisation, which uses calcium oxide
- Explain how car engines produce oxides of nitrogen, and describe how a catalytic converter removes them, e.g. 2CO + 2NO → 2CO2 + N2
- Describe photosynthesis as a reaction in which carbon dioxide and water combine to make glucose and oxygen, with chlorophyll present and drawing on energy from light
- Give the word equation and the symbol equation that represent photosynthesis