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E-factor: Environmental Impact Factor for Chemical Reactions

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Grade Range
Group Size
2-3 students
Active Time
45-60 minutes
Total Time
45-60 minutes
Area of Science
Green Chemistry
Key Concepts
chemical reactions, environmental impact factor (E-factor), waste, green chemistry, catalysts
Based upon the E-factor Lesson developed by Irv Levy, Gordon College

A chemical equation where the reactants are made of two groups of MM candies and the products are a large pile of MMs as the waste from the reaction and a pair of MMs as the desired product. thumb


In this lesson, students will do a simple exercise with M&Ms to understand what environmental impact factor (E-factor) is, how it applies to chemical processes, and how waste from chemical reactions can be reduced by applying the principles of green chemistry.

Learning Objectives

Students will:

NGSS Alignment


  • 15 small bags of M&Ms
  • 15 balances or digital scales
  • 30 cups
  • 15 calculators
  • Optional: plastic gloves
  • Bulk bag of M&Ms
  • 5 sealable plastic bags
  • Student worksheet

Background Information for Teachers

This section contains a quick review for teachers of the science and concepts covered in this lesson. Our partner Beyond Benign also offers additional training in the theory and practice of green chemistry in the classroom. Explore Beyond Benign's professional development opportunities.

The environmental impact factor (E-factor) relates to the 2nd Principle of Green Chemistry, Atom Economy. Frequently applied in an industrial sense, the E-Factor compares the amount of useful product to the amount of waste produced in a chemical process. It is calculated using the simple equation:

For more complex products, it is common to have a manufacturing process that has several chemical reactions. If each chemical reaction produces waste the resulting E-factor can be quite high.

The principles of Green Chemistry can be used to diminish the amount of waste created and lower the environmental impact factor of a particular chemical process. Watch the video to see what Green Chemistry is.

John Warner explains green chemistry

Green Chemistry Principles Addressed

  • Prevention: Design chemical syntheses to prevent waste, leaving no waste to treat or clean up.
  • Safer Solvents & Auxiliaries: Avoid using solvents, separation agents, or other auxiliary chemicals. If these chemicals are necessary, use innocuous chemicals.
  • Use of Renewable Feedstocks: Use raw materials and feedstocks that are renewable. Renewable feedstocks = farm products or the wastes of other processes; depleting feedstocks = fossil fuels (petroleum, natural gas, or coal) or are mined.
  • Reduce Derivatives: Avoid using blocking or protecting groups or any temporary modifications if possible. Derivatives use additional reagents and generate waste.
  • Catalysis: Minimize waste by using catalytic reactions. Catalysts are used in small amounts and can carry out a single reaction many times. They are preferable to stoichiometric reagents, which are used in excess and work only once.
  • Real-time Analysis for Pollution Prevention: Include in-process real-time monitoring and control during syntheses to minimize or eliminate the formation of byproducts.

Prep work

  • Prepare five baggies of M&Ms as shown below.
E-factor M&M model Industry segment
Clear bag full of green M&Ms with one yellow and five red M&Ms interspersed.


A chemical derived from Petroleum or natural gas

Example: Solvents detergents, adhesives

Clear bag full of green M&Ms with a handful of red, orange, and yellow M&Ms interspersed.

Bulk Chemicals

plastics and polymers

Example: plastic bottles, grocery bags

Clear bag full of green, yellow, brown, orange, and red M&Ms in near equal proportions.
Clear bag full of yellow, brown, orange, and red MMs in near equal proportions and only two green MMs.

Fine Chemicals

Chemicals used to make specific items

Example: coating on laptop screens, electronics parts

Clear bag full of yellow, brown, orange, and red M&Ms in near equal proportions and only one green M&M.


Example: antibiotics, blood thinners


  1. Show students the accompanying PowerPoint slides to explain E-factor and how it relates to a manufacturing process.
  2. Stop at slide 5!
  3. Ask students to get into groups of two or three.
  4. Give student worksheets to each group.
  5. Hand out a small bag of M&Ms to each group of students.
  6. Explain that this bag of M&Ms is very special but that unfortunately the only ones that you can use are the red ones.
  7. Following the directions on the student sheet, have students calculate the E-factor and answer the questions.
  8. Allow students to share their E-factor.
  9. Move onto slide 6, the challenge of using the 12 principles of green chemistry to reduce the E-factor.
    • Tell students they must come up with specific strategies of how they can reduce their waste in the lab.
  10. Move around the room and place a star by viable strategies that students have brainstormed.
  11. Have students share their ideas for waste reduction.
  12. Share next slides. Explain to students that for each strategy they have written down, they can remove one color from their waste pile.
    • Remind students that this only applies to strategies you have approved!
  13. Using their new product, have students recalculate their E-factor.
  14. Have students throw away any M&Ms left in their waste pile. They may eat their product and strategy M&Ms.
  15. Show students the prepared bags of M&Ms and explain how these bags represent chemical processes.
  16. Ask students if any of them use Ibuprofen. You may have to prompt them with over-the-counter brand names of the drug.
  17. Project the slide of the Ibuprofen.
  18. Explain that at the time Ibuprofen was invented it was a big breakthrough for people suffering from joint and muscle pain, it was originally invented to help arthritis patients. Sounds great right? Until you look at how much of the process created waste.
  19. With the old method, that means that there would be 68.72 tons of waste = 69 female walruses of waste.
  20. The process was changed in 1990 through the use of green chemistry techniques.
  21. Show the next slide with the new process. Ask the students to tell you what they immediately see as being different.
  22. Talk the students through the new process. Point out that the acetic acid is used as a catalyst.
  23. Point out that the current and better method = 13.33 tons of waste, 13 female walruses.
  24. In the new method, a mere 1% of the building block atoms result as waste. The new process also replaced a six-step with a three-step process, aiding energy efficiency (principle 6) and simplifying real-time analysis for pollution prevention (principle 11).
  25. Previously the waste went mostly to the landfill. Today, scientists look at the by-products too and think about how those by-products can be used to make something else rather than be discarded. It is just like when you have a Thanksgiving turkey. Try to imagine all the various foods you can make out of that one turkey.


You can collect and review, using the answer key, the students' worksheets as a way of assessing whether students understood the lesson.

Free science fair projects.