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14.5–14.6 Life Cycle Assessments and Reduce, Reuse, Recycle

GCSE Chemistry · AQA · Chapter 14: The Earth's Resources

A free GCSE Chemistry lesson for AQA (8462) from OBA School: assessing a product’s environmental impact from cradle to grave, and cutting the use of limited resources. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

  • Describe the four stages of a life cycle assessment (LCA)
  • Explain why some parts of an LCA are easy to measure and others need value judgements
  • Explain how selective LCAs can be misused, e.g. in advertising
  • Carry out a simple comparative LCA, such as for plastic and paper shopping bags
  • Describe how glass and metals (aluminium, steel, copper) are reused and recycled, and evaluate ways of reducing the use of limited resources and the pollution from mining

Key words

  • Life cycle assessment (LCA): A way of assessing the environmental impact of a product at every stage, from getting the raw materials to disposal.
  • Value judgement: A decision based on opinion about what matters most, rather than on measurements.
  • Reduce: Use less of a product or material in the first place.
  • Reuse: Use a product again for the same or another purpose, e.g. washing and refilling a glass bottle.
  • Recycle: Process a used material so it can be made into new products, e.g. melting scrap metal.
  • Limited resource: A raw material that will run out, e.g. metal ores, sand for glass, crude oil for plastics.

The stages of a life cycle assessment

A life cycle assessment looks at the environmental impact of a product over its whole life. At each stage it considers the use of energy, water and raw materials, and the waste and pollution produced. Transport and distribution are included at every stage.

To carry out an LCA you (1) list every input and output at each stage, (2) evaluate the environmental impact of each one, and (3) interpret the results to help choose between materials, products or processes.

Is an LCA objective?

  • The use of water, resources and energy, and the amount of some wastes, can be measured fairly easily.
  • Giving numbers to the effects of pollutants is much harder. For example, is a tonne of CO₂ worse than a litre of polluted water? This needs value judgements, so an LCA is not a purely objective process.
  • Selective or shortened LCAs can be used to support a conclusion that was decided in advance, for example in an advert that only mentions the stages where its product looks good.
  • Impacts happen on different scales: global (climate change, using up resources), regional (acid rain, smog) or local (polluting one stream). Deciding how much each should count is a judgement, not a measurement.
  • Where data are missing, estimates are used. A good LCA states the uncertainty (e.g. 120 ± 15 g of CO₂) and is checked by independent experts (peer review), especially if the company that makes the product paid for it.
  • An LCA looks at environmental impact only. It does not include the price or how well the product does its job.

Exam tip: If asked why an LCA might be biased, look at who paid for it, which stages were left out, and which effects needed value judgements.

A comparative LCA: shopping bags

  • Raw material; Plastic (polythene) crude oil or natural gas (finite); Paper wood from trees (renewable)
  • Energy to make (MJ); Plastic (polythene) 0.6; Paper 1.8
  • CO₂ released in making (g); Plastic (polythene) 40; Paper 120
  • Water used (dm³); Plastic (polythene) 0.3; Paper 2.4
  • Typical number of uses; Plastic (polythene) 4; Paper 1
  • Disposal; Plastic (polythene) not biodegradable; can be recycled; litter harms wildlife; Paper biodegradable; can be recycled or composted

Worked example: comparing per use

Plastic: 40 g ÷ 4 uses = 10 g of CO₂ per use. Paper: 120 g ÷ 1 use = 120 g per use.
120 ÷ 10 = 12

Answer: the paper bag releases 12 times as much CO₂ per use

But the plastic bag is made from a finite resource and lasts for hundreds of years as litter. Deciding which is “better” overall needs a value judgement.

Reduce, reuse, recycle

Metals, glass, building materials, clay ceramics and most plastics are made from limited raw materials, and much of the energy used to make them comes from fossil fuels. Quarrying and mining also damage the environment. Reducing use, reusing and recycling cuts the use of limited resources, energy use, waste and environmental impact.

  • Glass; Reuse bottles are collected, washed, sterilised and refilled; Recycle crushed, melted and made into new glass products
  • Metals; Reuse e.g. reclaimed steel beams; Recycle melted and recast or reformed into new products; scrap iron is added to make steel. Metals may need sorting and separating first.

Recycling different metals

  • Aluminium: extracting it from its ore needs electrolysis of molten aluminium oxide, which uses enormous amounts of electricity. Recycled aluminium only has to be melted, so it saves more than 90% of the energy, and conserves bauxite ore.
  • Iron and steel: scrap cars, machines and “tin” cans (steel with a thin tin coating) are easy to separate from other rubbish with a magnet. Using scrap saves energy (mostly from fossil fuels) in steel-making.
  • Copper: harder to recycle, because scrap copper is often mixed with other metals in alloys such as brass (copper and zinc). It must be purified by electrolysis before it can be used in electrical wiring. Clean copper wire can simply be melted and reused.

Why recycling metals matters for the environment. Most metal ores are dug from huge open-cast pits. Mining scars the landscape, makes noise and dust, destroys habitats and leaves heaps of waste rock; rain draining through exposed ore can make ground water acidic. Processing the ore also pollutes: smelting sulfide ores can release sulfur dioxide (acid rain), and making iron releases carbon dioxide. Every tonne of metal recycled means less mining and less of this pollution.

Worked example: energy saved by recycling

Making 1 tonne of steel from iron ore uses 25 GJ. Making it from scrap uses 10 GJ.
saving = 25 − 10 = 15 GJ; percentage saved = 15 ÷ 25 × 100 = 60%

Answer: 60% less energy

Key fact: Recycling still uses energy (collecting, sorting, transporting and melting), so reuse and reduce usually save more than recycling.

Common mistakes

  • Leaving out a stage of the LCA, especially use or disposal, or forgetting transport.
  • Saying an LCA is completely objective. Effects of pollutants need value judgements.
  • Assuming paper is always better because it is “natural”. Look at all the data, including energy, water and number of uses.
  • Saying an LCA includes cost. It compares environmental impacts only.
  • Saying recycling uses no energy. It uses less than making from raw materials, but collecting, sorting and melting all need energy.

Revision questions

Try these, then check your answers below each one.

Question 1. Why is a life cycle assessment not a purely objective process? (Choose from: Giving numerical values to the effects of pollutants needs value judgements, Energy use cannot be measured, Water use cannot be measured, Only plastic products can be assessed.)

Answer: Giving numerical values to the effects of pollutants needs value judgements

Working: Energy, water and resource use can be measured fairly easily, but judging how harmful pollutants are needs value judgements.

Question 2. Making 1 tonne of steel from ore uses 20 GJ; making it from scrap uses 8 GJ. What percentage of energy is saved by using scrap?

Answer: 60 %

Working: Saving = 12 GJ. 12 ÷ 20 × 100 = 60%.

Question 3. True or false? Glass bottles can be reused by washing, sterilising and refilling them.

Answer: True

Working: True. Glass bottles can be reused. They can also be recycled by crushing and melting them to make new glass products.

Related lessons

Continue in the full course

This lesson is section 14.5–14.6 (AGCCH1405) of our free GCSE Chemistry course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Chemistry course.

 

 

 

 

 

 

 

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