Key Stage 4 science · Chemistry – Chemical and allied industries

GCSE chemistry: life cycle assessment and recycling

Life cycle assessment is a way of judging the environmental impact of a product at every stage of its life, from getting the raw materials to throwing it away. At GCSE, students use it to compare products such as plastic and paper bags, and they judge when recycling a material makes sense. The topic is less about memorising facts and more about weighing evidence and justifying a conclusion, which makes it good practice for extended-answer questions.

Life cycle assessment and recycling, explained

A life cycle assessment, or LCA, breaks a product’s life into stages. The first is extracting and processing raw materials, such as mining ore or drilling for crude oil. Next comes manufacturing and packaging, then the use of the product, and finally disposal, which might be landfill, incineration or recycling. Transport can be counted at every stage. At each stage students consider the use of energy and water, the resources consumed, the waste produced and the pollution released, including carbon dioxide.

Some impacts can be measured, such as the mass of raw material or the energy used. Others are harder to put a number on, such as the damage caused by mining a landscape or the effect of waste on wildlife. Because of this, an LCA involves judgements, and the result depends on what has been included. A company comparing its own product with a rival’s can choose which stages count. Students learn to read such claims critically, asking who carried out the study and what was left out.

Recycling means turning used materials into new products so fewer raw materials are extracted. It can save energy and conserve limited resources, and it reduces the volume of waste going to landfill. Metals are often good candidates: recycling aluminium needs far less energy than extracting it from its ore, and metals can be melted and reformed many times. Glass can be recycled repeatedly too. Whether recycling is viable depends on collection and sorting, the cost and energy of the process, the quality of what can be made, and how much demand there is for the recycled product.

Plastics show the complications. There are many types, which must be sorted because mixing them can spoil the product, and some types can only be turned into lower-quality items, called downcycling. Paper fibres get shorter each time they are recycled, so they can only go round a limited number of times. The statutory objective is to understand why recycling is viable for some materials and not others, so schools tend to teach it through case studies rather than a single rule. Which ones your child sees is the school’s choice.

Words your child will hear

Life cycle assessment: A study of the environmental impact of a product at every stage, from raw materials to disposal.
Raw material: A natural resource that a product is made from, such as ore, crude oil or wood.
Finite resource: A resource that is being used far faster than it forms, so it will eventually run out, such as metal ores and crude oil.
Landfill: Disposal of rubbish by burying it in the ground.
Recycling: Processing used materials so they can be made into new products.
Downcycling: Recycling into something of lower quality or value than the original.
Sustainable: Meeting the needs of people now without stopping future generations from meeting their own needs.

What the National Curriculum says

The programme of study for Key Stage 4 says:

Students should be taught about life cycle assessment and recycling to assess environmental impacts associated with all the stages of a product's life
Students should be taught about the viability of recycling of certain materials

Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.

Try it: comparing two products

A shop considers switching from plastic carrier bags to paper carrier bags. Use a life cycle assessment to decide which has the lower environmental impact, and evaluate your conclusion.

Choose the stages: raw materials, manufacture, use, and disposal. Decide what to compare at each, such as energy used, water used and pollution released.
Raw materials and manufacture. Plastic bags come from crude oil, a finite resource, and need cracking and polymerisation. Paper bags come from trees, a renewable resource if forests are managed, but papermaking uses a lot of water and energy.
Use. Compare how strong each bag is and how many times it can be reused. A plastic bag that is used many times spreads its manufacturing impact across many trips, while a paper bag that tears after one trip does not.
Disposal. Plastic bags do not rot and can harm wildlife if littered, but can be recycled where collections exist. Paper rots down and can be recycled, though it may release methane in landfill.
Judge the evidence. The result depends on how many times each bag is reused and how it is disposed of. No single answer is correct for all situations, and any number-based study should say what was left out.

Neither bag is clearly better in every case. The impact per trip depends on how many times the bag is reused and what happens to it afterwards, so the best option is a bag reused as many times as possible and then recycled.

Common mistakes and how to help

Assuming recycling is always the best option

Recycling is promoted as good, so it seems always worthwhile.

What helps: Recycling uses energy and money too. It makes sense when the savings in raw materials and energy outweigh these, as with aluminium. For some materials, reducing and reusing come first. Ask “what is the alternative?” each time.

Thinking disposal is the only part of a product’s impact

Litter and landfill are visible, while mining, manufacturing and use happen elsewhere.

What helps: For products that use energy, such as cars or kettles, the use stage can have the largest impact of all. Ask your child to list every stage before deciding where the impact is.

Believing biodegradable means harmless wherever it ends up

The word suggests that something will vanish naturally.

What helps: Biodegradable items often need particular conditions such as heat, moisture and the right microorganisms. In landfill without air, some produce methane, a greenhouse gas. The label does not tell you where it is safe to throw it.

Expecting an LCA to give one correct answer

Science lessons often have a single right answer, so a judgement-based conclusion feels unfinished.

What helps: An LCA is about justified decisions. A good answer compares stages, uses evidence, states assumptions and admits what is uncertain. Practise writing “this suggests…, but it depends on…”.

How to help at home

Do a bin audit. For one week, glance at what your household throws away or recycles. Ask your child which items could have been reused, which could be recycled locally, and which are hard to recycle. Check your council’s guidance on what it accepts, since local rules differ.
Trace a product’s journey. Pick something small, such as a drinks can or a pair of trainers, and sketch its life from raw materials to disposal. Look at the label for where it was made. Then ask which stage probably has the biggest impact, and what you would need to know to be sure.
Sort metals with a magnet. Test a few clean food cans and drink cans with a fridge magnet. Steel cans stick, aluminium cans do not. Recycling plants use large magnets in the same way to pull steel out of mixed waste, which shows why sorting matters before processing.
Compare two real choices. Next time you choose between, for example, a reusable bottle and a bought one, or a glass jar and a plastic tub, talk it through using the stages. Notice that the answer often depends on how many times something is reused.

Builds on

Key Stage 3: Chemical reactions and equations
Key Stage 3: Acids, alkalis and neutralisation