Earth and atmosphere · GCSE Chemistry
Life cycle assessments
GCSE Chemistry revision on life cycle assessments: raw materials, manufacture, use, disposal, recycling, and how to compare products without pretending every number is exact.
An LCA follows a product from cradle to grave: extract, make, use, dispose. Energy, water, waste and pollution at each stage. Recycling can cut the extraction stage, but collection has a cost too.
The important bits
What you need to know
- 1
A life cycle assessment (LCA) measures the environmental impact of a product through raw-material extraction, manufacture, use, and disposal (or recycling).
- 2
Impacts to consider: energy and water use, consumption of finite ores and fuels, waste, and pollutant gases (CO₂, SO₂, NOₓ) at each stage — not only the factory chimney.
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Some parts of an LCA are hard to quantify (litter, visual impact, exact toxicity). That is why two LCAs of the same product can disagree, and why the exam wants a balanced comparison, not a fake precision.
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Plastic versus paper bags, disposable versus reusable bottles, and aluminium cans versus glass are the usual examples. The use phase matters: a cotton bag must be reused many times to beat a thin plastic bag.
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Recycling metals, glass and some plastics reduces the need to extract ores and often saves energy (especially aluminium versus electrolysis of bauxite). Transport and sorting still use energy.
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Reduce, reuse, recycle is the order: using less material beats recycling waste you did not need to make. Thinner packaging can cut impact if it still protects the food (food waste has its own footprint).
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Bioplastics and compostable packaging only help if they actually compost in real systems and if growing the crop did not simply shift land-use emissions. Evaluation must be honest.
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Link to other pages: aluminium LCA is dominated by electrolysis energy unless the metal is recycled; paper LCA includes water and energy in the mill; petrol-car use phase is dominated by CO₂ from combustion.
Quotations worth analysing
Short evidence. Real method.
“Extract → manufacture → use → dispose.”
A table with those four headings is how you structure a six-mark compare. Leave one stage out and you will miss a mark even if your chemistry is fine.
“Recycling aluminium uses a small fraction of the energy of extracting it from bauxite.”
Electrolysis of Al₂O₃ in cryolite is electricity-heavy. Melting scrap aluminium skips that. Collection lorries still burn fuel — include them, but they rarely cancel the saving.
“Not all impacts can be measured easily.”
This sentence is often worth a mark. Then give an example: litter in rivers, or the exact harm of a mixture of plastic additives. Do not invent a number for it.
Go deeper
Compare the same job, not the same mass
One plastic bag versus one cotton bag is the wrong comparison if the cotton bag is used 200 times and the plastic bag once. An LCA should compare delivering shopping, or containing 330 cm³ of drink, over a realistic lifetime. Glass is heavier to transport than aluminium or PET, so the use/distribution stage can dominate. Paper bags tear when wet and may need more material. Students pick a favourite material and ignore the use phase. The mark scheme wants at least one advantage and one disadvantage for each option, tied to a stage of the life cycle, then a reasoned choice with a condition (“if reused at least n times”).
Go deeper
Quantified energy versus unquantified harm
Kilowatt-hours, kilograms of CO₂ and litres of water can be estimated. The death of marine animals from a particular piece of litter cannot be put in the same spreadsheet honestly. GCSE wants you to say that LCAs still help because they stop us looking only at the factory, but they have uncertainties and value judgements (is water use in a dry country worse than extra CO₂?). When data are given in a table, use the table — do not override it with a slogan. If plastic scores lower CO₂ but higher persistent waste, say both and then judge against the question’s priority.
Go deeper
Chemistry content that actually belongs in an LCA answer
Name a process: electrolysis of aluminium, reduction of Fe₂O₃ with carbon (CO₂ from the blast furnace and from the carbon), polymerisation of crude-oil fractions, chlorination of water, combustion in use (CₓHᵧ + O₂ → CO₂ + H₂O). Those sentences show you are still in a Chemistry exam. Then disposal: landfill (methane if organic waste rots anaerobically), incineration (energy recovered but CO₂ and possibly toxins if poorly controlled), recycling (melt and remould). Phytomining and bioleaching can appear if the product is copper. Keep it specific. “Bad for the environment” is not an LCA.
See the idea in action
Compare an aluminium drinks can with a reusable steel bottle using LCA stages. Extraction: aluminium from bauxite needs electrolysis (high energy) unless recycled scrap is used; iron ore is reduced with carbon (CO₂). Manufacture: rolling and forming both use energy. Use: the bottle must be washed (water, heating) but replaces hundreds of cans; the can is single-use. Disposal: cans recycle well and recycling saves most of aluminium’s electrolysis energy; a bottle that is thrown away after a month loses its advantage. Limitation: transport distances and washing frequency are hard to know exactly. Conclusion: the bottle is better if reused many times; a once-used bottle is worse than a recycled can.
Exam technique
Turn knowledge into marks
Use the four stages as paragraph headings. Give a numerical or named process impact where you can, admit what is hard to quantify, and finish with a judgement that depends on reuse or recycling. Link aluminium to electrolysis energy.
Common mistakes
Do not give these marks away
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Only discussing disposal, or saying recycling has no environmental cost.
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Declaring one material “eco-friendly” without a stage-by-stage comparison or a reuse condition.
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Ignoring the use phase (washing, fuel in a car, number of times a bag is used).
What is a life cycle assessment in GCSE Chemistry?
AA test of how long a battery lasts
BAn evaluation of a product’s environmental impact from raw materials through use to disposal
CA method of extracting aluminium
DA measure of pH only
Show the answer
An evaluation of a product’s environmental impact from raw materials through use to disposal. An LCA covers extraction, manufacture, use and disposal (or recycling), including energy, waste and emissions. Some impacts are hard to quantify.
Quick questions
If this is the bit you searched
What is a life cycle assessment GCSE Chemistry?
A way of assessing the environmental impact of a product through extracting raw materials, manufacturing, using and disposing of it. Recycling can be included as an alternative to disposal.
Why can LCAs give different answers for the same product?
Some impacts are hard to measure, different assumptions are made about reuse and transport, and people value different harms (CO₂ versus litter) differently.
Why does recycling aluminium score well in an LCA?
Extracting aluminium by electrolysis uses a large amount of electrical energy. Recycling melts scrap metal and avoids most of that energy use and bauxite mining.
Is a paper bag always better than a plastic bag?
Not necessarily. Paper can use more energy and water to make and may need to be thicker. An LCA must include manufacture, whether it is reused, and disposal, not just the word “paper”.