AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Students should be able to carry out simple comparative LCAs for shopping…
Full specification wording
Life cycle assessment: Students should be able to carry out simple comparative LCAs for shopping bags made from plastic and paper.
A simple comparative LCA sets the same stages side by side for two products.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 5 of 5
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A simple comparative LCA sets the same stages side by side for two products. For plastic and paper bags, compare raw materials, manufacture, use and disposal. Paper comes from trees, needs water and energy to pulp and form, and may be recycled or composted. Plastic comes from crude oil, needs energy to polymerise and mould, and may be reused many times before disposal. A fair comparison uses the same functional unit, such as carrying the same shopping for one year, and the same stages. Data might show paper uses more water and energy in manufacture, while plastic persists as litter. The conclusion depends on how many times each bag is reused and which impacts are weighted most.
What earns the marks
- Set out the four LCA stages for both paper and plastic bags.
- Use a common functional unit, such as carrying a fixed amount of shopping for one year.
- Compare at least two quantified inputs or outputs, such as water, energy, raw material or waste.
- Consider reuse: a plastic bag used many times has a lower impact per shopping trip.
- Reach a justified conclusion that depends on the assumptions and weightings used.
Common mistakes and how to put them right
Comparing one paper bag with one plastic bag without considering reuse.
Put it right by using a functional unit over time.
Ignoring the extraction stage for one material.
Put it right by covering all four stages for both.
Giving a conclusion without stating the assumptions.
Put it right by linking the conclusion to the data and weightings.
Exam tips
- Present the comparison in a table with the same stages as rows.
- State the functional unit before comparing numbers.
- Finish with a conclusion that names the deciding factor, such as reuse or water use.
Try the lesson
The start of the Life cycle assessment: Students should be able to carry out simple comparative LCAs for shopping bags made from plastic and paper. lesson, made from checked teaching notes for this specification point.
Have a go first
A student carries out a simple comparative Life Cycle Assessment (LCA) for a plastic shopping bag and a paper shopping bag. Which statement provides a valid comparison of their environmental impacts?
Listen
A simple comparative LCA sets the same stages side by side for two products. For plastic and paper bags, compare raw materials, manufacture, use and disposal. Paper comes from trees, needs water and energy to pulp and form, and may be recycled or composted. Plastic comes from crude oil, needs energy to polymerise and mould, and may be reused many times before disposal. A fair comparison uses the same functional unit, such as carrying the same shopping for one year, and the same stages. Data might show paper uses more water and energy in manufacture, while plastic persists as litter. The conclusion depends on how many times each bag is reused and which impacts are weighted most. A strong answer earns marks for these points. Set out the four LCA stages for both paper and plastic bags. Use a common functional unit, such as carrying a fixed amount of shopping for one year. Compare at least two quantified inputs or outputs, such as water, energy, raw material or waste. Consider reuse: a plastic bag used many times has a lower impact per shopping trip. A common slip: Comparing one paper bag with one plastic bag without considering reuse. Instead, using a functional unit over time. Exam tip: Present the comparison in a table with the same stages as rows.
See it
Key words
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Comparative LCA
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Functional unit
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Materials from crude oil and plants
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See every definition
- Comparative LCA
- A simple comparison that sets the same stages side by side for two products, such as shopping bags made from plastic and paper.
- Functional unit
- The same basis used to make a comparison fair, such as carrying the same shopping for one year.
- Materials from crude oil and plants
- Plastic comes from crude oil, while paper comes from trees.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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